Free tool
Loan interest calculator
Work out the interest on a loan for any dates, daily or a twelfth of the year at a time, simple or added to the loan. Or build a monthly repayment schedule. Every figure is shown month by month, to the cent.
Interest
Period
Balance at the end
| Period | Days | Opening balance | Interest | Closing balance |
|---|
Monthly instalment
Total interest
Total paid
| Month | Opening balance | Instalment | Interest | Capital | Closing balance |
|---|
How the calculator works out the interest
Interest = Balance × (Rate ÷ 365) × Days
- Daily charges each day at a 365th of the yearly rate, so a 31-day month costs more than a 30-day one. Most South African loan agreements work this way.
- A twelfth of the year charges the same each full month. A part month gets its share by days.
- Simple interest is only ever charged on the balance you enter. Added to the loan puts each month's interest onto the balance at month-end, so it earns interest from then on.
- The days run from the first date up to the second, the way most agreements count them. Each month is rounded to the cent, with the part-cents carried on, so the months add up to the total.
- The repayment schedule uses equal monthly instalments at a twelfth of the yearly rate, and the last instalment clears exactly what is left.
The worked examples behind these sums are in our guides: How to calculate interest on a loan, day by day and Loan amortisation schedules explained. Once you have the figure, here is how to post it to Xero.
This calculator is a guide. Your loan agreement decides how interest is charged, including how days are counted and when a rate changes. It does not handle repayments or rate changes part way through a period; Loanbooq does, for every loan, every month.