How to use this calculator
- Enter the loan amount, annual interest rate and term.
- Add optional extra payments: a fixed extra amount every month, a yearly lump sum, or a one-time payment in a specific month.
- Review the annual and monthly tables, or download them as CSV for your spreadsheet.
Formula
Each month, interest is the outstanding balance times the monthly rate. The rest of the payment, plus any extra payment, reduces the principal.
Interest_k = Balance_(k−1) × r
Principal_k = Payment − Interest_k + Extra_k
Balance_k = Balance_(k−1) − Principal_k
First month of a $200,000, 30-year loan at 6%
- Monthly payment = $1,199.10; monthly rate r = 0.5%.
- Interest = 200,000 × 0.005 = $1,000.00.
- Principal = 1,199.10 − 1,000.00 = $199.10, so the new balance is $199,800.90.
Frequently asked questions
What is an amortization schedule?
It is a table showing every payment on a loan, how much of each goes to interest and principal, and the remaining balance afterwards.
Why do I pay so much interest at the beginning?
Interest is charged on the outstanding balance, which is largest at the start. As you pay down principal, the interest share of each payment shrinks.
When is the yearly extra payment applied?
In this calculator it is applied with every 12th payment (months 12, 24, 36 and so on).