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Numbers & Calculators

Loan Installment Calculator

Compare monthly installments under a flat rate and an effective rate before you apply for a motorbike, car, mortgage (KPR) or business loan, and see the month-by-month amortization table.

Free · no sign-up · runs in your browser · updated

Use Loan Installment Calculator

Interest method

Enter the loan, interest and term to see the simulation.

How to use Loan Installment Calculator

  1. Enter the loan amount, the annual interest rate and the term in months.

  2. Choose the interest method: flat or effective (annuity). Enter an origination fee if there is one.

  3. Read the monthly installment, total interest, total payment and the amortization table.

Flat rate versus effective rate

With a flat rate, interest is calculated on the original principal for the whole term: total interest = principal × annual rate × term (years), then principal and interest are split evenly across the months. With an effective (annuity) rate, interest is calculated on the remaining principal, which shrinks every month, so the interest share is large at first and falls over time, while the installment stays the same.

Because the remaining principal keeps falling under a flat rate while interest is still charged on the original principal, a flat rate is actually much more expensive than its nominal figure suggests. This tool shows the equivalent effective rate so that comparisons between offers are fair.

What is not included

Origination fees, insurance, administration and late-payment penalties vary by lender. The results here are a simulation; the official installment follows the loan agreement from your bank or financing company.

Questions about Loan Installment Calculator

What is the formula for a flat-rate installment?

Monthly installment = (principal + principal × annual rate × term in years) ÷ number of months. Example: a Rp12,000,000 loan at a 12% flat rate per year over 12 months: interest Rp1,440,000, installment Rp1,120,000 per month.

What is the formula for an effective-rate (annuity) installment?

Installment = P × i ÷ (1 − (1 + i)^−n), where P is the principal, i is the monthly rate (annual rate ÷ 12) and n is the number of months. The installment stays fixed, and its split shifts from interest to principal over time.

Why is a 1% flat rate per month not the same as a 1% effective rate per month?

A flat rate is calculated on the original principal for the whole term even though the principal keeps falling, so its effective rate is much higher, typically about 1.7 to 2 times the flat rate. Use the equivalent effective rate to compare.

Will this match the installment from my bank?

It can differ slightly because of rounding, origination fees, insurance and how days are counted. Treat it as an initial estimate.

Is my loan data sent to a server?

No. The calculation runs in your browser.

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