How Our Calculators Work

Every GoalCalcs calculator turns the numbers you enter into an estimate using standard financial formulas. This page sets out, for each one, how it calculates, what it assumes and the sources behind its rates and rules, so you can check the work and see why a result may differ from a lender's quote.

How we check the math

Each calculator's formulas are tested against independent reference calculations: worked examples and separate month-by-month simulations, computed apart from the calculator's own code.
Those tests run automatically before every update, and an update that fails any of them doesn't go live.
Results are worked out in your browser, from the numbers on the page.

Why a lender's figures can differ

Many card issuers charge interest daily, on each day's balance; the calculators charge it monthly.
Your quote reflects your own credit, down payment, fees and the day it was given; our starting rates are national averages.
Property tax, insurance and HOA dues change from year to year; the calculators hold them steady.
Payment dates, rounding and fees in your loan agreement can all change the totals.

Rates and limits we use

Market figures change, so each one carries the date or year it applies to.

30-year fixed mortgage rate: 7.28% for the week of Oct 1, 2026; Freddie Mac's weekly average for borrowers with 20% down and strong credit. The Mortgage and Home Affordability calculators move to the newest week when they load.; Source: Freddie Mac Primary Mortgage Market Survey
15-year fixed mortgage rate: 6.6% for the week of Oct 1, 2026; The same survey's 15-year average, the starting rate on the 15-year mortgage calculator.; Source: Freddie Mac 15-year average on FRED
Conforming loan limit, 2026: $832,750 for a single-family home in most counties, up to $1,249,125 in high-cost areas; Above it, a conventional loan is a jumbo loan. The ZIP lookup shows your county's limit.; Source: FHFA conforming loan limits for 2026
FHA loan limits, 2026: $541,287 to $1,249,125 for a single-family home, by county; FHA can't insure a loan above the county's limit.; Source: HUD FHA loan limits for 2026
FHA mortgage insurance: 1.75% of the base loan upfront, plus 0.15% to 0.75% a year; The annual rate depends on the term, the loan size and the down payment.; Source: HUD Mortgagee Letter 2023-05
Private mortgage insurance (PMI): 0.38% to 1.2% of the loan a year, by credit score; Our planning estimates for conventional loans with less than 20% down, not quotes. Your lender's rate depends on your credit, down payment and insurer.

Mortgage Calculator

Estimates your full monthly housing payment (principal and interest, property tax, home insurance, HOA dues and mortgage insurance) plus closing costs, total interest and how extra payments move your payoff date.

How it calculates

Loan amount = price − down payment. An FHA loan adds HUD's upfront premium, 1.75% of that amount, and financed closing costs are added too.
Principal and interest use the standard amortization formula at your rate ÷ 12 over the term in months.
Property tax is your percentage of the price, mill rate (dollars per $1,000 of price) or dollar amount, ÷ 12. Insurance is the yearly premium ÷ 12, and HOA dues are added as entered.
A conventional loan above 80% of the price adds PMI: your PMI rate × the loan amount ÷ 12. The results show when you can ask to cancel it (your balance reaches 80% of the original value) and when it ends on its own (the original schedule reaches 78%, or the loan's midpoint).
An FHA loan adds HUD's annual premium on the base loan instead, at HUD's rate for the term, loan size and down payment: on a loan over 15 years and up to $726,200, 0.55% a year with less than 5% down and 0.5% with 5% or more. It lasts 11 years with 10% or more down, otherwise for the life of the loan.
Closing costs = the origination fee (a percentage of the loan) plus the appraisal, title and other fees.
Pay off by a set year searches for the smallest recurring extra payment, to the cent, whose schedule ends by December of that year. It keeps any other extra payments you entered and runs the same schedule as the results, so the PMI dates and the savings match them.
The starting rate is Freddie Mac's weekly 30-year average: 7.28% for the week of Oct 1, 2026. The page moves to the newest week when it loads.

What it assumes

A fixed rate, with tax, insurance and HOA amounts that stay the same every year. In practice they usually rise.
PMI as a flat yearly rate on the loan amount, 0.75% unless you change it. That is an estimate; your lender's quote depends on your credit and down payment.
FHA's annual premium on the original base loan. HUD works it out on each year's average balance, so later years are slightly overstated here.
The starting rate is a national average for borrowers with 20% down and strong credit. Enter the rate you are quoted.
Above the 2026 national limits ($832,750 conforming, $541,287 FHA), whether a loan fits depends on the county; the ZIP lookup shows your county's limit.

Sources

Copy and figures last reviewed Oct 2, 2026.

The same method runs the 15-Year Mortgage Calculator and FHA Mortgage Calculator, which start from different inputs.

Open the Mortgage Calculator

Home Affordability Calculator

Works backward from your income, debts and savings to the highest home price whose full monthly payment fits two income limits, one for housing and one for housing plus your other debts, and whose cash to close fits your savings.

How it calculates

Housing budget = the lower of two limits: gross monthly income × the housing ratio, and gross monthly income × the total-debt (DTI) ratio − your monthly debt payments.
Principal and interest, mortgage insurance and a percentage property tax all grow in step with the price, so the price that uses the whole budget is solved directly. It is then checked at that price, in case PMI or FHA's premium changes there.
Principal and interest assume a fixed-rate loan over the term you pick: 30, 20 or 15 years. The rate starts from Freddie Mac's weekly 30-year average (7.28% for the week of Oct 1, 2026), or its 15-year average (6.6%) for a 15-year loan, with a 20-year loan halfway between, and is adjusted for credit: on a conventional loan, from 0.1 points lower for exceptional credit to 0.5 points higher for poor. Enter your own quote to replace it.
A conventional loan above 80% of the price adds PMI by credit tier and down payment: at 5% down, from 0.38% a year for exceptional credit to 1.2% for poor, less with more down and more at 3% down. An FHA loan adds HUD's 1.75% upfront premium and its annual premium.
If you enter savings, the price is also capped so the down payment and, unless you finance them, the closing costs (origination fee plus appraisal, title and other fees) fit. The lower of the two limits wins.

What it assumes

Comfortable, the default, is the traditional 28/36 guideline: housing up to 28% of gross income and housing plus debts up to 36%. Lender max uses Fannie Mae's 45% total for manually underwritten loans on a conventional loan, and FHA's standard 31% housing and 43% total. Custom lets you set both (above 50%, Fannie Mae's limit for automated underwriting, conventional loans generally can't be approved).
A 30-year term unless you pick 20 or 15 years. A shorter term costs less interest but raises the payment, so the same budget buys less house. No weekly survey covers 20-year loans, so that rate is an estimate between the 15- and 30-year averages.
PMI rates are planning estimates, not quotes: the steps between down-payment bands follow MGIC's published borrower-paid rate card. Tiers: exceptional 800–850, very good 740–799, good 670–739, fair 580–669, poor below 580.
Property tax, insurance and HOA dues as entered, the same every year.
Your monthly debts are the minimum payments you owe now, before the new mortgage.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the Home Affordability Calculator

Refinance Calculator

Compares keeping your current loan with replacing it: the new monthly payment, the change from today, the month your savings cover the closing costs, and the interest left on each path.

How it calculates

Works out your current monthly principal and interest. From the years left, it is the payment that clears your balance in that time; from the original loan, it is the payment on your note. Either way: P = L × r ÷ (1 − (1 + r)^−n), with r the annual rate ÷ 12 and n the number of months.
Pays down your current balance at that payment, month by month, to find when it ends and the interest still to come.
Sizes the new loan (your balance, plus any cash out, plus the closing costs if you add them to the loan) and finds its payment with the same formula at the new rate and term.
Adds up the difference between the two payments each month until it covers the closing costs: that month is the break-even.
Compares the lifetime cost: interest on the new loan plus closing costs, against the interest left on the current loan. When the payment falls but this total rises, the results say so.

What it assumes

Both loans are fixed-rate with monthly payments, and each month's interest is the annual rate ÷ 12 on the balance.
Principal and interest only: property taxes, home insurance and mortgage insurance are left out, since they come with the home either way.
No prepayment penalty on the current loan, and no adjustment for inflation or for what the money could earn elsewhere.
The new rate starts at Freddie Mac's weekly 30-year average, which tracks purchase loans to borrowers with good credit and 20% down; your quote may differ.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the Refinance Calculator

Bi-Weekly Mortgage Calculator

Compares paying a mortgage monthly with paying half the monthly payment every two weeks: the payoff dates, the time saved and the interest saved.

How it calculates

Monthly payment M = L × r ÷ (1 − (1 + r)^−n), with L the loan amount, r the annual rate ÷ 12 and n the term in months. The bi-weekly payment is M ÷ 2.
Interest is charged every two weeks at (1 + r)^(12/26) − 1, the rate that compounds to the same yearly cost as the monthly rate.
Each half-payment covers that period's interest, and the rest reduces the balance, until the loan is paid off; the last payment is only what is still owed.
Interest saved is the monthly plan's total interest minus the bi-weekly plan's. Bi-weekly payment dates fall every 14 days from the first payment date.

What it assumes

Each half-payment is credited the day it arrives. Servicers differ: one that holds half-payments and credits them monthly saves somewhat less, which the results also show (modeled as one-twelfth of the payment extra each month).
A fixed rate, no fee for the bi-weekly plan, and principal and interest only (no taxes or insurance).
Checked against an independent calculation: $100,000 at 5% over 30 years, paid $268.41 every two weeks, ends after 656 payments (about 25.2 years) with $75,893.94 of interest.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the Bi-Weekly Mortgage Calculator

HELOC Calculator

Estimates the line of credit your equity could support, the interest-only payment while you draw, the payment once repayment starts, and the total interest.

How it calculates

Line of credit = home value × the lender's borrowing limit − your mortgage balance.
Interest-only payment = amount borrowed × rate ÷ 12, paid every month of the draw period.
Repayment payment = D × r ÷ (1 − (1 + r)^−n): the level payment that clears the amount borrowed, D, over the n months of the repayment period at the monthly rate r.
Total interest adds the interest-only payments to the interest in the repayment schedule. The payment jump is the repayment payment minus the interest-only one.
Also works out the repayment payment at a rate 2 percentage points higher, to show what a rising variable rate can do.

What it assumes

You borrow the full amount at the start and keep it through the draw period, paying only interest; borrowing less, or later, costs less.
One rate for the life of the line. HELOC rates are usually variable, so real payments move with the index.
No annual fees, closing costs or introductory rate, and repayment in equal monthly payments rather than a balloon.
The default rate is the U.S. prime rate on its date (Federal Reserve H.15), a common HELOC index; lenders add a margin.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the HELOC Calculator

Rent vs. Buy Calculator

Compares the full cost of buying a home and selling it when you move with renting a similar home for the same years, counting what the money could have earned if invested.

How it calculates

Buying: the down payment and closing costs up front; then each month the mortgage payment (fixed rate, at the yearly rate ÷ 12), property tax and upkeep as a share of the home's value, insurance, HOA dues, and with less than 20% down, PMI on the original loan until the schedule reaches 78% of the price or the loan's midpoint.
Renting: rent plus renters insurance each month.
Once a year the home's value rises by the home price growth, and property tax, upkeep, insurance and HOA dues with it; rent and renters insurance rise by the rent increase.
Both paths spend the same: the renter invests the down payment and closing costs, and whichever path costs less in a month invests the difference, at the investment return, compounded monthly.
When you move, the home sells at its grown value, less selling costs and the remaining loan balance.
Net cost of buying = everything paid to buy and own + what that money could have earned − what the sale brings back. Net cost of renting = rent and renters insurance + what any extra rent could have earned. The difference is how much more one path leaves you with.
The break-even year is the first year in which buying's net cost is lower, checked for every year up to 50.
The main drivers raise each yearly rate (home price growth, investment return, mortgage rate and rent increase) by one percentage point, one at a time, and show how far each moves the result.

What it assumes

Taxes are left out: the mortgage interest deduction, tax on investment gains and tax on the home sale.
Monthly costs are counted at the start of each month.
Growth rates stay the same every year, and the mortgage rate is fixed.
You sell the home when you move.
The default mortgage rate is Freddie Mac's latest weekly 30-year average. The other defaults are examples, not forecasts; closing costs default to 3%, within the 2% to 5% range the CFPB gives.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the Rent vs. Buy Calculator

Loan Calculator

Works out the fixed payment that repays a loan over its term, the total interest, and a payment-by-payment schedule, including how extra payments shorten the loan.

How it calculates

Turns the yearly rate into a rate per payment. With monthly compounding and monthly payments, that is the rate ÷ 12. Other choices go through the effective yearly rate, (1 + rate ÷ n)^n − 1 for n compounding periods a year, then the matching rate for 12, 26 or 52 payments a year.
Finds the level payment with the standard amortization formula: payment = loan × r ÷ (1 − (1 + r)^−N), where r is the rate per payment and N the number of payments. At 0%, it is simply the loan ÷ N.
Builds the schedule one payment at a time: interest is the balance × r, the rest of the payment reduces the balance, and any extra payment goes straight to principal.
Stops when the balance reaches zero. The last payment is only what is still owed, and interest saved compares the schedule with and without your extra payments.
Solving for the loan amount turns the formula around: loan = payment × (1 − (1 + r)^−N) ÷ r, rounded down to the cent. Solving for the term counts the payments, N = −ln(1 − r × loan ÷ payment) ÷ ln(1 + r), then builds the schedule for the exact number and the smaller last payment. A payment that doesn't cover the first month's interest never repays the loan, and the calculator says so.

What it assumes

A fixed rate for the whole term, with every payment made in full and on time.
No fees, insurance or prepayment penalties. Check your loan agreement for those.
Bi-Weekly and Weekly split the same loan into 26 or 52 payments a year over the same term. The "accelerated" bi-weekly plan is different; to model it, keep Monthly and add an extra payment of one-twelfth of your payment.
Amounts are rounded for display, so a lender's figures can differ by a few cents a payment.

Sources

CFPB: What is amortization and how could it affect my auto loan?

Copy and figures last reviewed Oct 2, 2026.

Open the Loan Calculator

Auto Loan Calculator

Works out the monthly payment, total interest and total cost of a car loan with your trade-in, rebate, sales tax and fees, or the price a monthly payment can buy.

How it calculates

Taxable price = vehicle price − trade-in value (or the full price, if your state taxes it). A manufacturer's rebate comes off first only if you say your state taxes the price after the rebate. Sales tax = taxable price × your tax rate.
Amount financed = price − rebate − down payment − trade-in value + what you still owe on the trade-in + sales tax + title and registration fees. Owing more than the trade-in is worth puts that negative equity into the new loan. Paying tax and fees upfront leaves them out of the loan and adds them to what is due at signing, with the down payment.
The payment uses the standard amortization formula at the APR ÷ 12 over the term in months, and the schedule rounds each payment and each month's interest to the cent. Total of payments = amount financed + total interest.
Price for a payment: the loan a payment repays is payment × (1 − (1 + r)^−n) ÷ r. The amount financed rises in step with the price, so the price follows exactly, rounded down to the cent so the payment stays within your budget.
0% APR or the rebate: works out the same car twice, once at the dealer's rate and term without the rebate and once with the rebate at your rate and term, and compares the total cost of each.
Extra payments go straight to principal, month by month, to show the earlier payoff and the interest saved.

What it assumes

Sales tax and fees are added to the loan unless you choose to pay them upfront.
Sales tax is charged on the price before a manufacturer's rebate unless you turn that off. That is the rule in many states, including California and Washington, while Minnesota takes the rebate off first; check your state's rule.
A fixed rate and on-time payments. Dealer add-ons such as extended warranties or GAP coverage are left out unless you add them to the price.
Total cost counts the price after any rebate, tax, fees, negative equity paid through the loan and interest.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the Auto Loan Calculator

Credit Card Payoff Calculator

Shows how long it takes to pay off a card balance, and how much interest you pay, with the card's shrinking minimum payment or with a fixed amount each month.

How it calculates

Each month, interest = balance × APR ÷ 12, rounded to the cent as a statement shows it.
Minimum payment: the month's interest plus a percentage of the balance (1% unless you change it, the formula most large issuers use), or a flat percentage that already includes the interest. It is never less than the dollar floor ($35 unless you change it) or more than you owe.
Fixed payment: the same amount every month, with the last payment only what is left.
Each payment covers the month's interest first and the rest reduces the balance, month after month until it is paid, for up to 100 years.
With a fixed payment, the results compare it with paying only the minimum under your card's terms, and flag a fixed payment below this month's minimum.

What it assumes

No new purchases, fees or rate changes while you pay the balance down.
Interest uses APR ÷ 12 on the month's balance. Most issuers charge a daily rate on each day's balance, which comes out close but not identical.
A payment that doesn't cover the month's interest never pays the card off, so the results say so instead of showing a date.

Sources

CFPB: How does my credit card company calculate the amount of interest I owe?

Copy and figures last reviewed Oct 2, 2026.

Open the Credit Card Payoff Calculator

Debt Payoff Planner

Compares two ways to pay off several debts, highest rate first (avalanche) and smallest balance first (snowball), with paying only the minimums.

How it calculates

Monthly budget = all your minimum payments + the extra amount you enter. It stays the same every month.
Each month, every debt adds interest at its APR ÷ 12 and then gets its minimum payment.
The rest of the budget goes to the target debt: the highest APR for the avalanche, the smallest balance for the snowball. When a debt is paid off, its minimum rolls into the next target.
This repeats until every debt is paid, for up to 100 years, recording each payoff month and the interest each debt cost.
The minimums-only comparison pays each debt exactly its minimum, with no extra and no rollover.
Debt-free by a set month searches for the smallest extra a month, to the cent, that has the chosen strategy pay off every debt by that month, running the same month-by-month plan as the results.
Debts loaded from My Accounts start at their balance today: each account's last statement balance, then every payment due since (the ones marked missed or different as marked) and any extra payments, charges and fees logged. Their planned extra payments land in the month of the payment they come off with.

What it assumes

Each minimum payment stays as entered. Card minimums shrink as the balance falls, so for a card this is like keeping today's minimum as a fixed payment.
No new borrowing, fees or rate changes.
Interest is the APR ÷ 12 on each month's balance, and payoff dates count whole months from today.

Sources

CFPB: How does my credit card company calculate the amount of interest I owe?

Copy and figures last reviewed Oct 2, 2026.

Open the Debt Payoff Planner

Balloon Loan Calculator

Works out the monthly payment on a balloon loan, amortizing or interest only, and the lump sum still owed when the loan term ends.

How it calculates

Terms can be in years or months; a term in years is that many years × 12 months.
Amortizing: sizes the monthly payment as if the loan ran the full amortization period, with the standard amortization formula at the rate ÷ 12 over that many months, rounded to the cent.
Interest only: each payment is that month's interest, the balance × rate ÷ 12, so it repays none of the loan.
Runs the schedule only to the end of the loan term. Each month, interest is the balance × rate ÷ 12, rounded to the cent, and the rest of the payment, plus any extra payment, reduces the balance.
The balloon is the balance left after the last scheduled payment; on an interest-only loan, that is the amount borrowed less any extra payments. On that date you owe the final payment plus the balloon.

What it assumes

A fixed rate until the balloon is due, and every payment made in full and on time.
On an interest-only loan, an extra payment lowers the balance, so the payments after it are smaller.
No fees and no refinancing. How you pay the balloon (cash, a new loan or a sale) is up to you.
On an amortizing loan, the loan term is no longer than the amortization period.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the Balloon Loan Calculator

APR Calculator

Works out a loan's annual percentage rate from its amount, interest rate, term and lender fees, by the actuarial method in Regulation Z, and shows the amount financed and finance charge.

How it calculates

Finds the monthly payment: P = L × r ÷ (1 − (1 + r)^−n), where L is the loan amount (plus the fees, if you add them to the loan), r the interest rate ÷ 12 and n the number of months.
Subtracts the prepaid finance charges from the loan to get the amount financed, A.
Solves for the monthly rate i at which the payments, discounted back to the day you borrow, equal the amount financed: A = P × (1 − (1 + i)^−n) ÷ i. It narrows in on i by repeated halving until it is exact to well under a millionth of a percent.
APR = i × 12. The finance charge is the total of payments minus the amount financed.

What it assumes

Equal monthly payments, the first one month after the loan is made: no odd first period or adjusted final payment, which a lender's own figure may include.
A fixed interest rate for the whole term.
Only the fees you enter count. Title insurance, appraisal, credit report and similar real-estate fees are left out of the finance charge when they are reasonable, so leave them out here.
Checked against Regulation Z appendix J's worked example ($5,000 repaid in 24 monthly payments of $230 is 9.69%) and an independent high-precision calculation.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the APR Calculator

Savings Calculator

Projects a savings balance from a starting amount, regular deposits and an APY, year by year, and works out the deposit needed to reach a goal.

How it calculates

Turns the APY into the rate for each deposit period: (1 + APY)^(1/n) − 1, where n is 52, 26, 12 or 1 deposits a year. Compounded n times, that rate earns exactly the APY over a year.
Each period, adds the deposit at the start, then credits that period's interest on the new balance, rounded to the cent.
Raises the deposit once a year by the yearly increase, rounded to the cent.
Adds up each year's deposits and interest for the yearly table. The future value is the last year's ending balance, so the table and the headline always match.
For a goal, solves for the first-year deposit that reaches it in time, rounded up to the cent, and steps the plan as entered forward, up to 100 years, to find the month it gets there.
The inflation-adjusted value divides the future value by (1 + inflation rate)^years.

What it assumes

The rate stays the same for the whole period.
Deposits go in at the start of each period, and interest is credited each period, to the cent.
No taxes, fees or withdrawals.
A bank that credits interest on a different schedule may show a balance a few cents different.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the Savings Calculator

Compound Interest Calculator

Grows a starting amount and regular deposits at a quoted interest rate and compounding, and shows the balance, deposits and interest year by year.

How it calculates

Turns the quoted rate into an effective yearly rate: (1 + r/m)^m − 1, where m is 365 for daily, 12 for monthly, 4 for quarterly and 1 for yearly compounding. A rate entered as an APY is used as it is.
Turns that yearly rate into the rate for each deposit period: (1 + yearly rate)^(1/n) − 1, where n is 52, 26, 12 or 1 deposits a year. When deposits and compounding share a schedule, that is exactly r/m.
Each period, adds the deposit at the start or the end, as chosen, and credits that period's interest, rounded to the cent.
Adds up each year's deposits and interest for the yearly table; the balance shown is the last year's ending balance.

What it assumes

The rate stays the same for the whole period.
When deposits and compounding run on different schedules, each deposit earns the equivalent rate for the time it is invested.
Interest is credited each deposit period, to the cent.
No taxes, fees or withdrawals.

Sources

CFPB: Regulation DD (Truth in Savings), Appendix A, Annual Percentage Yield Calculation

Copy and figures last reviewed Oct 2, 2026.

Open the Compound Interest Calculator

Retirement Calculator

Projects retirement savings to the age you plan to retire, in future and today's dollars, and the monthly income they could pay at a withdrawal rate.

How it calculates

Works out this year's contributions: a dollar amount, or a share of salary; the employer match is the match rate times your contribution, up to the match limit, as a share of salary.
Each month, adds a twelfth of the year's contributions at the end of the month, rounded to the cent, and credits growth at (1 + expected return)^(1/12) − 1, rounded to the cent.
With contributions set as a share of salary, both yours and your employer's rise each year by the yearly raise. A dollar amount stays the same.
Today's dollars divide the balance at retirement by (1 + inflation)^years.
Monthly income is the balance at retirement times the withdrawal rate, divided by 12, in future and in today's dollars.

What it assumes

Social Security, pensions, taxes and investment fees are left out.
The return is the same every year; real returns vary.
IRS contribution limits are not applied; a note appears when this year's contribution is over the 401(k) limit for your age.
The 4% withdrawal rate is a rule of thumb from US market history, not a guarantee.

Sources

Copy and figures last reviewed Oct 2, 2026.

Open the Retirement Calculator

Found a mistake?

If a result or a figure here looks wrong, please tell us, with the numbers you entered and where your figure comes from.