Calculators

Change any field and the results update instantly. Nothing is stored, submitted, or sent anywhere - the maths runs entirely in your browser.

How the calculation works

This uses the standard amortising-loan formula, the same one lenders use for fixed-rate products:

M = P × [ r(1+r)^n ] / [ (1+r)^n - 1 ]

Where M is the monthly payment, P the principal, r the monthly interest rate (annual rate divided by twelve) and n the number of monthly payments.

What it deliberately leaves out

• Property taxes and homeowners insurance, usually escrowed with a mortgage payment
• Private mortgage insurance, typical below 20% down
• HOA or condo dues
• Origination fees, discount points and closing costs

For a mortgage, the real monthly outgoing is often several hundred dollars above the principal-and-interest figure. Treat this as the borrowing cost, not the housing cost.

Three ways to use it well

1. Compare terms, not payments. Run 15 and 30 years and look at total interest.
2. Test the rate you were quoted against the benchmark on the rates page.
3. Stress-test affordability. Add a point to the rate and check the payment still works.