Amortization Calculator

Every payment on a fixed-rate loan is the same size, calculated with the standard amortization formula: M = P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ − 1], where P is the loan amount, r is the monthly interest rate, and n is the number of payments.

Worked example: a $350,000 loan at 6.5% over 30 years. Monthly rate r = 0.065 ÷ 12 = 0.005417, n = 360. The formula gives a payment of $2,212.24/month. In month 1, interest is $350,000 × 0.005417 = $1,895.83, so only $316.40 goes to principal. By year 25, most of that same $2,212.24 payment goes to principal instead.

Because each month's interest is calculated on whatever balance is left, paying down principal faster — through an extra payment — reduces every future month's interest charge too, which is why extra payments save more than their face value in total interest.

An extra $200 a month applied in year 1 of a 30-year loan removes principal that would otherwise sit on the books accruing interest for close to three more decades. The same $200 applied in year 28 only prevents two years of interest on that amount — the math still helps, just far less dramatically.

This is also why refinancing resets the clock in a way that can work against you: a refinance restarts the schedule back at mostly-interest payments, even if the new rate is lower. Our Refinance Calculator compares the full picture, not just the new monthly payment.

Checking a lender's numbers: confirming the payment schedule a lender or loan estimate shows you actually matches the loan amount, rate, and term you agreed to.

Deciding whether to pay extra: seeing the exact time and interest an extra monthly payment would save before committing to it long-term.

Any fixed-rate loan, not just mortgages: the same math applies to an auto loan, a personal loan, or a student loan — anywhere payments are fixed and interest accrues on a shrinking balance.

Comparing to a full mortgage payment: if you need property tax, insurance, and PMI included, our Mortgage Calculator covers the full monthly payment, not just principal and interest.

Total interest is everything you pay over the life of the loan minus what you borrowed. Work out the monthly payment, multiply it by the number of payments, then subtract the original loan amount.

Example: a $200,000 loan at 6% over 30 years has a monthly payment of about $1,199.10. Over 360 payments that adds up to about $431,676, so the total interest is roughly $231,676. The calculator above shows this figure for any loan, along with the year-by-year schedule.