What this calculator does
It works out the monthly payment of a loan, how much of every payment is interest and how much repays the loan, and what the whole loan costs. Type the amount, the yearly interest rate and the term, and the result and a full payment schedule appear as you type. Nothing is sent anywhere: the maths runs in your browser, in whole cents, so the totals are exact to the cent instead of "close enough".
The calculator is currency-neutral. It suits a mortgage, a car loan, a student loan or a personal loan in any currency; pick a currency code if you want the symbol and the right number of decimals, or leave it on plain numbers.
How to use it
- Enter the loan amount, the interest rate per year and the term, in years or in months. A rate of 0 is allowed.
- Choose the repayment style. "Equal monthly payments" is the usual mortgage and car-loan kind, called an annuity: every payment is the same. "Equal principal" repays the same slice of the loan each month plus interest on what is left, so the first payments are the largest and they fall over time. Many banks quote loans this way.
- Optionally add an extra amount you will pay every month, and a start date to see a calendar date next to every payment.
- Read the result on the right and the schedule below it. Copy the schedule as CSV or download it to open in a spreadsheet.
Numbers can be typed either way: 1,234.56 and 1.234,56 are both understood, and the tool shows how it read a number whenever the two styles could be confused.
A worked example
Borrow 200,000 at 6% a year for 30 years. The monthly rate is 6% divided by 12, which is 0.5%, so the first month's interest is 200,000 x 0.005 = 1,000.00. The payment is 1,199.10, so only 199.10 of the first payment repays the loan and the balance falls to 199,800.90. Interest is charged on the remaining balance each month, so the split turns around slowly: after 5 years the balance is still 186,108.80, and after 10 years it is 167,371.60. Over 360 payments you pay 231,677.04 in interest and 431,677.04 in total, more than twice what you borrowed.
A shorter term changes the picture sharply. The same loan over 15 years has a payment of 1,687.71 and costs 103,788.82 in interest.
How the rounding works
Money is held in whole cents, never in floating-point numbers. The payment is the standard annuity formula rounded half up to the cent. Each month's interest is the balance times the monthly rate, also rounded half up to the cent. Because the payment is rounded, the balance would not land on exactly zero after the last scheduled payment, so the last payment is whatever clears it. In the example above the last payment is 1,200.14 instead of 1,199.10. A bank may round differently, for example always down, so a lender's own schedule can differ by a few cents. The method is stated here so you can reproduce every row.
An extra amount is added to every payment and goes straight to the principal. In the example, adding 200 a month ends the loan after 252 payments instead of 360, which is 9 years sooner, with a last payment of 702.08. Interest falls from 231,677.04 to 151,876.18, a saving of 79,800.86. The tool shows both the time and the interest saved. Before you rely on this, check with your lender that early repayment carries no fee and that extra money is applied to the principal.
Equal principal or equal payments
Take 12,000 at 12% a year over 12 months. With equal principal you repay 1,000 of the loan every month plus interest: the first payment is 1,120.00, the last is 1,010.00, and the total interest is 780.00. With equal payments, every payment is 1,066.19 and the total interest is 794.23. The falling schedule costs a little less interest because the balance shrinks faster, but it asks for more cash at the start. Which one suits you depends on your budget, not on the arithmetic.
What it does not do
The calculator models a standard fully repaying loan with monthly payments made at the end of each month and a fixed rate. Variable rates, interest-only periods, balloon payments, fees, insurance, taxes and daily-interest conventions are not included, and a real quote can differ. Treat the result as an estimate to compare options, not as financial advice or an offer. To check a percentage on its own, use the percentage calculator, and to work on a downloaded schedule in other software, the CSV and JSON converter can turn it into JSON.
