How it works
Most car loans, personal loans and mortgages are amortizing loans: you pay the same amount every month, and each payment first covers that month’s interest and then reduces the balance. Early payments are mostly interest; later payments are mostly principal.
The monthly payment formula (EMI)
M = P × r ÷ (1 − (1 + r)−n)where P is the amount borrowed, r is the monthly rate (yearly rate ÷ 12 ÷ 100) and n is the number of monthly payments. With a 0% rate the payment is simply P ÷ n.
Worked example. 100,000 borrowed at 6% a year for 30 years: r = 0.06 ÷ 12 = 0.005 and n = 360. M = 100,000 × 0.005 ÷ (1 − 1.005−360) = 599.55 a month. In the first month the interest is 100,000 × 0.005 = 500.00, so only 99.55 reduces the balance. Over 30 years you pay about 115,838 in interest — more than the amount borrowed.
How the schedule is calculated
Every month: interest = remaining balance × r, rounded to the cent; principal = payment − interest; new balance = old balance − principal. All money is calculated in whole cents to avoid rounding drift, and the final payment is adjusted so the balance ends at exactly zero. Download the full table as a CSV file to open in Excel or Google Sheets.
Extra payments
Adding an extra amount each month goes straight to the principal, so the loan ends earlier and the total interest falls. In the example above, an extra 100 a month pays the loan off in 252 months instead of 360 — 9 years early — and saves about 39,900 in interest. Check first whether your lender charges an early-repayment fee.
What this calculator does not include
It assumes a fixed rate for the whole term and monthly payments. It does not add fees, insurance, property tax or administration charges, and it does not model variable rates or “flat-rate” loans where interest is charged on the original amount. Ask your lender for the annual percentage rate (APR) to compare offers fairly.
Saving instead of borrowing? See the compound interest calculator. To check what share of your income a payment takes, use the percentage calculator.