Loan payment calculator
Work out the monthly payment on a loan or mortgage and, above all, how much you will end up paying in interest.
Your figures
Result
- Amount borrowed$150,00065.9%
- Interest$77,66634.1%
- Total interest
- $77,666
- Total you will repay
- $227,666
- Extra cost over the principal
- 51.8%
- Number of payments
- 360
- Of the first payment, interest
- $375.00
- Of the first payment, principal
- $257.41
What we assume
- Level amortising payments: the payment stays the same for the life of the loan.
- The rate entered is the nominal annual rate, and the monthly rate is that divided by 12.
- The rate is assumed fixed. On a variable-rate mortgage the payment changes at each review.
- Fees, insurance and set-up costs are not included. The real cost will be somewhat higher.
- That is why the APR on your offer will be higher than the nominal rate you enter here.
How it is calculated
With level payments you always pay the same amount, but what it is made of changes every month. Interest is charged on the principal you still owe, so early on almost all of the payment is interest and only a small part reduces the debt. Over time the proportion flips.
The payment comes from this formula:
payment = C x i / (1 - (1 + i)^-n)
where C is the principal, i the monthly rate and n
the number of months.
The uncomfortable figure
Look at the breakdown of the first payment. On a 150,000 loan at 3% over 30 years, of the 632 you pay in month one, 375 is interest and only 257 reduces the debt. That is exactly why overpaying early saves so much.
An example
A 150,000 mortgage at 3% over 30 years costs about 632 a month. Over the full term you repay roughly 227,000, of which 77,000 is interest: half as much again as you borrowed.
Frequently asked questions
Why is the APR higher than the rate I entered?
Because the APR folds in fees, insurance and set-up costs, while the nominal rate is only the interest. Two loans with the same nominal rate can have very different APRs.
What happens if I overpay?
You can either shorten the term or lower the payment. Shortening the term almost always saves more interest, because you stop paying interest sooner.
Does this work for a variable-rate mortgage?
Only as a snapshot at the current rate. When the rate is reviewed the payment is recalculated on the outstanding balance and the remaining term.
Keep calculating
All tools →- Loan amortisation schedule Every payment broken down. The interesting part is not the total, it is watching how long it takes before you are mostly paying off the debt.
- Early repayment: term or payment One lump sum, two ways to use it. Which saves more interest is not close, but the other one has its reasons.
- How much mortgage can I afford Two things limit you: what you can pay each month and what you have saved. We tell you which one is binding, because that decides what to do about it.
- From nominal rate to APR The nominal rate is what they advertise; the APR is what compares. Here is the real APR, with the arrangement fee spread across the life of the loan.
- Debt-to-income ratio The figure a lender looks at before any other. Not how much you earn, but how much of it is already spoken for.
Updated on 2026-08-26. Calculations run in your browser; nothing you type is sent to a server.