Financial calculators that show their work

Every tool here publishes its formula, ships with a worked example checked against a known answer, and cites the primary source behind any external figure. Free, no sign-up — and it does not advise.

Mortgage calculators

Mortgage Payment CalculatorWork out monthly principal and interest on a fixed-rate mortgage, total interest over the term, and how much of the first payment reduces the balance.Extra Payment CalculatorSee how many payments an extra principal payment removes and how much interest it saves, across a ladder from $50 to $1,000 a month, on your own figures.Refinance Break-Even CalculatorFind the month a lower rate has recovered the closing costs, see your cumulative position year by year, and test how small a rate cut stops being worth it.How Much House Can I Afford?Work backwards from income and debt to a maximum purchase price, shown under four debt-to-income bands so you can see whose judgement sets the ceiling.Biweekly Mortgage Payment CalculatorPay half your mortgage every two weeks: the new payoff date, interest removed, and how much saving comes from the schedule rather than the extra month.Mortgage Points Break-Even CalculatorHow long a discount point takes to break even, and how much that answer moves when the rate reduction is smaller — the number no lender publishes in advance.15-Year vs 30-Year Mortgage CalculatorCompare 15-year and 30-year terms on the same monthly outflow, price the difference invested, and find the return where the 30-year path pulls ahead.PMI Removal Date CalculatorWhen private mortgage insurance ends on a conventional loan: the 80% date you can request, the 78% automatic date, and how much extra principal moves each.Mortgage Recast CalculatorEnter the balance, the rate, the months left and the lump sum. See the new required payment, the extra interest it costs, and what recasting gives up.Down Payment CalculatorEnter the price, your down payment and the rate. See the monthly payment, how long insurance runs, and what a smaller down payment costs over the life.FHA vs Conventional Loan CalculatorEnter the price, the down payment and the conventional rate. See the FHA upfront and annual premiums priced against conventional PMI, and the FHA rate at which the two break even.Closing Cost CalculatorEnter the price, the down payment and what each end of the trade costs. See the round trip as one number, the price the house has to reach to cover it, and how long that takes.FHA Loan Costs CalculatorEnter the price, the down payment and the years you keep the loan. See the FHA upfront premium, the annual premium rate that applies to your loan-to-value, how many months it runs, and what the insurance costs in total.True Monthly Mortgage Payment (Principal, Interest, Tax, Insurance, HOA)Add property tax, homeowners insurance and HOA dues to the principal-and-interest payment so the figure is the amount that actually leaves your account, not the financeable-only number the built-in search calculator returns.How Much House Can I Afford? (PITI — Tax, Insurance and HOA Included)Work backwards from income and debt to a maximum purchase price, then subtract your own property tax, homeowners insurance and HOA before pricing the loan — the figure the built-in search affordability tool overstates because it treats the whole budget as principal and interest.FHA Mortgage Payment Calculator (Upfront & Annual MIP Included)Computes the full monthly FHA payment — principal, interest and the mortgage insurance FHA makes mandatory — including the 1.75% upfront premium rolled into the loan and the annual premium that, at the 3.5% down FHA is known for, runs for the full 30 years rather than the 11 years often quoted.How Much House Can I Afford with an FHA Loan? (Mandatory Mortgage Insurance Included)Works backwards from income to the most house an FHA loan can buy at FHA's 3.5% minimum down — counting the 1.75% upfront premium financed into the loan and the annual premium that comes out of the monthly payment, both of which the built-in search affordability tool leaves out.Points vs. More Down Payment: Where the Same Cash Goes FurtherCompare buying discount points against putting the same cash into your down payment. The test is net worth on the day you sell, not the monthly payment — and the answer turns on how much rate each point actually buys.2026 Conforming Loan Limit: Where Your Loan Sits Against the LineEnter the price, your down payment and your county. 3,075 of the 3,235 US counties share one 2026 limit — $832,750 — so the real question is how far your loan sits from it, and how much more down payment would put it back under. Both answered here.How Long You Pay PMI: The Rate Sets the ClockOn one $400,000 loan with 3.5% down, mortgage insurance runs 99 months at a 3% rate and 161 months at 8%. The table prices every rate band, the 20% down payment cliff, and what extra principal can and cannot move.

Loan calculators

Auto Loan CalculatorCalculate a car's amount financed with sales tax and trade-in, the monthly payment, total interest, and the real cost of a 72- or 84-month term.Credit Card Payoff CalculatorSee how long a credit card balance takes to clear on minimum payments, what each extra dollar removes, and how paying a fixed 3% or 5% of the balance compares.

Investing and growth calculators

Compound Interest CalculatorSee the future value of a lump sum plus monthly contributions, how it splits between what you paid in and what compounding added, and when it crosses over.Retirement Savings CalculatorProject a retirement balance from savings and contributions, then convert it to monthly income at 3.5%, 4% and 4.5% withdrawal rates, with IRS limits.CAGR CalculatorConvert two values into a compound annual growth rate, see how long a rate takes to double or triple your money, and what the annualised figure hides.Inflation and Purchasing Power CalculatorSee what a sum will buy after inflation, what the same basket will cost, how long purchasing power takes to halve, and your real return net of inflation.401(k) Employer Match CalculatorSee what the employer match pays in at each rate, what staying below the match limit leaves unclaimed, and what that money would become by retirement.How much more can you put into a 401(k) and IRA this year?Enter what you have already contributed and your age. See your remaining 401(k) and IRA room for 2026 and 2027, and whether the Roth catch-up rule blocks your super catch-up.

Savings calculators

Savings & APY CalculatorConvert a quoted savings rate into the effective annual yield, see what each compounding adds, and compare it with the FDIC national deposit rate.Goal Savings CalculatorWork backwards from a target to the monthly saving it requires, and see the second target inflation creates: the same figure with purchasing power held.Savings Rates vs Credit Card RatesThe national average savings rate is 0.38% a year and the average credit card rate is 20.94%. Enter your own card balance and monthly payment and see what the spread costs on a balance you name.

What makes these different

Two things are true about almost every free calculator online: you cannot see the formula, and you cannot see where the numbers came from. FigureDeck is an attempt to fix both.

Where to start

The mortgage cluster is the most developed. Start with the payment calculator if you have a loan amount and a rate in mind, the affordability calculator if you are working from income instead, the extra-payment tool if you already have a mortgage and are asking whether overpaying is worth it, and the break-even tool if you are weighing a refinance.

The loan tools cover instalment credit — cars and revolving balances — where the arithmetic of stretching a term, or of paying only the minimum, produces results most people do not expect. The savings and investing tools handle compounding, effective annual yield and annualised returns.