About AmortGrid
What AmortGrid is
AmortGrid is a free suite of 12 mortgage, loan and debt calculators. It covers mortgage payments, full amortisation schedules, extra payments, home affordability, deposits and down payments, refinancing, auto loans, student loans, personal loans, debt payoff, credit card payoff and compound interest. Every calculator runs in your browser: you enter your figures, the page computes the instalment, the total interest and the payment schedule, and nothing is uploaded to a server.
Who it is for
AmortGrid is for anyone in the United States or the United Kingdom who needs a straight answer about borrowing. That includes first-time buyers working out what they can afford, homeowners deciding whether to overpay or refinance, borrowers comparing a 15-year term against a 30-year term, and anyone who wants to check a lender's or broker's figures before signing. You do not need an account, an email address or any financial documents to use it.
Why we built it
A mortgage is usually the largest financial commitment a household ever makes, yet the tools people use to understand it are often slow, crowded with advertising, or unwilling to explain where their numbers come from. We wanted the opposite: a calculator suite that loads quickly, works on a phone, explains its assumptions in plain English, and treats your financial information as yours rather than ours.
How we work
Every formula is implemented once, in a single calculation module, and covered by an automated unit test suite. The payment formula, the balance formula and the rounding rule each exist in exactly one place, so a correction fixes every calculator at once and cannot drift out of step between pages. Reference cases are checked against published figures: a $300,000 loan at 6.5% over 30 years must produce a monthly payment of $1,896.20, and the closed-form balance calculation is verified against a period-by-period simulation to within a cent.
We publish our method openly. The methodology page sets out the amortisation formula and the meaning of every symbol, the nominal-rate convention and why we use it, how extra payments are applied, the affordability ratios, the rounding policy, the testing policy and what our models deliberately do not attempt to predict. Because results are computed client-side, the amounts you type in never leave your device.
AmortGrid is independent. We are not owned by, funded by or operated on behalf of a bank, mortgage lender, broker or lead-generation network. No lender reviews our calculations, and no commercial partner decides what our guides say.
Our principles
- One formula, one implementation. Each calculation is written once and covered by tests, so a fix in one place fixes every calculator.
- Publish the method. The formula, the rate convention, the assumptions and the known limitations are written down for anyone to check.
- Your inputs stay yours. Calculations happen in your browser. We do not transmit, store or sell the amounts, income or debts you enter.
- No account, no paywall. No sign-up and no email address are required to see a result.
- Independence. Advertising and affiliate relationships never change a calculation, a result or the wording of a guide, and any commercial relationship is disclosed where it appears.
- Corrections come first. A report that a figure is wrong takes priority over everything else in our queue.
What we do not do
We do not give financial advice, and we do not arrange, broker, originate or sell loans. The calculators produce estimates from the figures you supply. Our disclaimer and terms of service explain the limits of the site, and the contact page explains how to tell us when a number looks wrong.
Last reviewed 2026-09-27.