Loan instalment calculator

What you can set

You enter the loan amount, the number of instalments (in months), the nominal interest rate per year and the instalment type: equal or decreasing. Under the extra options you can add a commission, as an amount or as a percentage of the loan amount, and say whether it is added to the loan or charged at the start.

The starting values are an example to edit, not a bank offer. The fields accept amounts from 100 to 10,000,000, a term of 1 to 600 months and a rate from 0% to 100% (with a decimal point or comma; pasted numbers with spaces work too).

Equal and decreasing instalments

With equal instalments every payment is the same size: at first you mostly pay interest, and over time more of each payment goes towards the principal. With decreasing instalments the principal part is constant, so the first instalment is the highest and the following ones fall. Decreasing instalments usually give a lower total interest, but they need a higher payment at the start.

Nominal rate, not APRC

You enter the nominal rate, which is the annual rate quoted in the bank's offer. Do not enter the APRC here: it also includes costs such as commission, so it is usually higher. You can work out an indicative APRC in the separate APRC calculator.

What the results mean

The instalment is the monthly payment (for decreasing instalments we show the first and the last one). Total interest is the interest across the whole schedule. Cost of credit is interest plus fees, without the principal. Total to repay is the loan amount plus the cost of credit. Sum of instalments is the total of all instalments; when the commission is added to the loan, it equals the total to repay.

Worked example

A loan of 20,000 at a nominal rate of 12% a year, over 36 months, equal instalments and no commission. The monthly rate is 12% ÷ 12 = 1%. The calculator shows an instalment of 664.29, a sum of instalments of 23,914.31 and total interest of 3,914.31. The formula without rounding the instalments gives 3,914.30; the difference of one cent comes from rounding each instalment to the cent.

What the calculator does not include

We don't include insurance, periodic fees, a variable interest rate or your creditworthiness. This is a simulation of a hypothetical scenario, not a bank offer and not an assessment of your chances of getting a loan. You can compare bank offers in the comparison tool.

Equal (annuity) instalments: P = A × r × (1+r)^n / ((1+r)^n − 1), where A is the balance to be repaid, r is the monthly rate (annual rate ÷ 12) and n is the number of instalments. Decreasing instalments: the principal part is constant (A ÷ n) and interest is calculated on the falling balance, so the first instalment is the highest.

Each month's instalment and interest are rounded to the cent, and the last instalment absorbs the remainder, so the schedule adds up exactly to the result. A commission added to the loan increases the balance the instalments are calculated on; a commission charged at the start reduces the amount you receive. We calculate in equal months (no dates or day counts) at a fixed rate for the whole term.