How to use the loan calculator
- Enter the Loan amount, the Interest rate (% per year) and the Loan term in years or months. Any currency works.
- Choose the Repayment type: equal monthly payments, equal principal payments, or interest only with the loan repaid at the end.
- Read the monthly payment, the total interest and the total amount paid. The bar shows how much of everything you pay is principal and how much is interest.
- The Repayment schedule lists each year or month with the payment, its principal and interest parts, and the balance still owed. Download CSV saves the table for Excel or Google Sheets.
The three repayment types
Equal monthly payments (amortizing)
Every payment is the same: P × r ÷ (1 − (1 + r)^−n), where P is the amount borrowed, r the monthly rate (annual rate ÷ 12) and n the number of months. Interest is charged on the outstanding balance, so early payments are mostly interest and later ones mostly principal. Most mortgages, car loans and personal loans work this way.
Equal principal payments
The balance falls by the same amount every month and interest is added on what is left, so the first payment is the largest and each one after is slightly smaller. The result box shows the first and the last payment. You pay less interest in total, but need more money at the start.
Interest only, repay at the end
You pay only interest each month and the whole amount in the final payment, sometimes called a bullet or balloon repayment. Monthly costs are lowest, but because the balance never shrinks, total interest is highest.
Worked examples
A loan of 250,000 at 5% a year – the calculator's starting values – compares like this:
| Repayment type and term | Monthly payment | Total interest | Total paid |
|---|---|---|---|
| Equal payments, 30 years | 1,342.05 | 233,139.46 | 483,139.46 |
| Equal payments, 15 years | 1,976.98 | 105,857.13 | 355,857.13 |
| Equal principal, 30 years | 1,736.11 → 697.34 | 188,020.83 | 438,020.83 |
| Interest only, 30 years | 1,041.67, last 251,041.67 | 375,000.00 | 625,000.00 |
Look at how the first years are weighted towards interest: of the first 1,342.05 payment, 1,041.67 is interest and only 300.39 reduces the balance, and after 10 of the 30 years you still owe 203,355.16. Halving the term raises the payment by about 47% but cuts the total interest by more than half.
How extra payments shorten a loan
Money paid on top of the scheduled amount goes straight to principal. Next month's interest is then charged on a smaller balance, so more of every later payment also goes to principal and the effect builds on itself. In the example above, paying 200 extra each month (1,542.05 instead of 1,342.05) clears the loan in 22 years and 7 months instead of 30 years and saves about 65,736 in interest.
The calculator has no extra-payment field, but you can still use it for this:
- For a one-off prepayment, take the balance from the schedule, subtract the prepayment and enter the result as a new loan over the remaining term. That shows the lower payment if your lender keeps the end date.
- To see what a faster payoff saves, shorten the term until the monthly payment is the most you can comfortably pay.
Check first whether your loan charges an early-repayment fee.
Tips
- The calculator assumes a fixed rate charged monthly. Variable-rate loans change over time, and some lenders count interest daily, so expect small differences from an official quote.
- Fees, insurance and property taxes aren't included. Where you can, compare offers by APR (annual percentage rate), which folds most fees into one figure.
- The balance column tells you what you would still owe if you sold or refinanced in a given year.
- To see what the same monthly amount would grow to if you saved it instead, try the Compound Interest Calculator.
FAQ
Which repayment type costs least?
At the same rate and term, equal principal payments cost the least interest, equal monthly payments a little more and interest-only the most. Equal payments are still popular because they are easier to budget.
Why is so much of the early payment interest?
Interest is charged on the balance, which is highest at the start. As the balance falls, the interest part of each payment shrinks and the principal part grows.
Can I use it for a mortgage?
Yes, for the loan itself. A real monthly housing payment may also include property tax, insurance and other charges collected by the lender.
What is in the CSV file?
One row per year or month, matching the view you have chosen, with the payment, principal, interest and balance to two decimal places.
These figures are estimates for planning, not financial advice. Your lender's documents are what count.