About RateCalc

What this site is

RateCalc is a set of free finance calculators and everyday utilities — mortgages, loans, compound interest, FIRE projections, retirement, debt payoff, rent-vs-buy, plus unit converters and date tools.

There are no accounts, no sign-up walls, and no lead-generation forms. We do not sell your details to a lender, because we never collect them in the first place.

How the math works

Every calculation runs in your browser. Nothing you type is sent to a server — there is no server-side calculation and no API that receives your numbers. You can verify this by opening your browser’s network tab while using any calculator.

The formulas are standard, published finance formulas rather than proprietary models:

Mortgage and loan payments use the standard amortizing-annuity formula,P × r(1+r)ⁿ / ((1+r)ⁿ − 1), where r is the monthly rate and n the number of payments. The zero-interest case is handled separately as P / n.
Compound interest uses future value of a lump sum plus an annuity-immediate for monthly contributions, iterated month by month so that contribution increases can be modelled.
FIRE and savings goals solve the same future-value equation for the number of periods, in closed form.
PMI is charged only while the loan-to-value ratio is above 80%, and drops off automatically in the projection once it is not.

How the numbers are checked

Each formula is implemented as a pure function with a fixed set of validation cases, and those cases run automatically on every change to the site. A $400,000 mortgage at 7.00% over 30 years, for example, is pinned at $2,128.97 per month, and the suite fails if a change moves it by more than a cent.

Rounding happens only at the point of display. Intermediate steps use full double-precision arithmetic, which is why our figures may differ by a few cents from calculators that round at each step.

What these calculators do not do

This matters more than the features list, so it is worth being direct:

They are estimates, not quotes. Your actual mortgage payment depends on your lender, credit profile, escrow arrangement, and closing costs.
State-level figures are averages. The state mortgage pages use a single statewide effective property-tax rate and average insurance premium. Your county, city, school district, exemptions, and assessed value will all move the real number.
Investment returns are assumptions, not forecasts. The default rates are long-run historical averages. Markets do not deliver an average return every year.
Tax handling is simplified. The rent-vs-buy model assumes full itemization and does not model the SALT cap or AMT.
This is not financial advice. It is arithmetic. For decisions of any size, talk to a qualified professional who knows your circumstances.

Who builds it

RateCalc is an independently built and maintained project — not backed by a lender, broker, or insurer, and it does not receive referral commissions from any financial institution. That independence is the reason there are no “check your rate” buttons anywhere on the site.

Running costs are covered by advertising. See the privacy policy for exactly what that does and does not mean for your data.

Corrections

If you think a number is wrong, please tell us — include the calculator and the exact inputs you used and we will check it against the formula. Getting the arithmetic right is the whole point of the site.