Reducing Balance Loan Calculator

Calculate a reducing-balance loan the way banks really do it: interest each month is charged only on the remaining balance, so every installment pays down more principal. Enter your loan amount, annual rate and term to see the monthly payment, total interest and a full month-by-month schedule. Compare a flat rate against reducing balance, or add extra principal to see how much faster you clear the loan — all in your browser, free.

Loan amount (principal) *

฿

Annual interest rate (%) *

The nominal per-year rate. Interest each month is charged on the remaining balance.

Term *

months

Number of monthly installments (1–600).

Flat rate to compare (%) — optional

Enter a flat (add-on) rate to see how much more a flat-rate loan would cost.

Extra principal per installment (฿) — optional

฿

Pay this much on top of each installment to see a shorter term and interest saved.

Your repayment plan will appear here

Enter the loan amount, interest rate and term to see the installment and schedule.

Monthly installment

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Total interest

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Total repayment

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Amortization schedule

No.	Payment	Interest	Principal	Balance

Early installments are mostly interest; principal grows each month as the balance falls. The final row is rounded so the balance reaches zero.

How to use

Enter the loan amount (principal), the annual interest rate and the term in months.
Read your monthly installment, total interest and total repayment instantly.
Optionally enter a flat rate to see how much more a flat-rate loan would cost.
Optionally add extra principal per installment to see a shorter term and interest saved.
Review the amortization schedule, then Copy summary or Export CSV.

Features

Accurate reducing-balance installment using the standard amortization formula
Full month-by-month schedule of payment, interest, principal and balance
Flat rate vs reducing balance comparison showing the true extra cost
Extra-principal payoff: shorter term and total interest saved
THB-formatted results with copy summary and CSV export
100% in-browser — your figures never leave your device

Frequently asked questions

What is a reducing balance loan?

A reducing-balance (ลดต้นลดดอก) loan charges interest only on the outstanding balance, which falls each month as you repay principal. Because the balance shrinks, the interest portion of each installment drops and more goes to principal over time.

How is the monthly installment calculated?

The level payment is M = P·r·(1+r)^n ÷ ((1+r)^n − 1), where P is the principal, r is the monthly rate (annual rate ÷ 12) and n is the number of months. This keeps the installment constant while the interest and principal split changes each month.

Is a flat rate cheaper than reducing balance?

Almost never. A flat rate charges interest on the full original principal for the whole term, so a 3.5% flat rate is roughly equivalent to a much higher reducing-balance rate. This tool shows the exact extra interest a flat rate costs.

How much do I save by paying extra each month?

Any amount added to the principal each installment shortens the term and cuts total interest, because you reduce the balance interest is charged on. Enter an extra amount to see the new payoff term, months saved and interest saved.

Does this calculator send my data anywhere?

No. Every calculation runs locally in your browser. Nothing you type is uploaded, stored or shared, and the tool works without any sign-up.

Reducing Balance Loan Calculator

Flat rate vs reducing balance

Paying extra each month

Amortization schedule

How to use

Features

Frequently asked questions

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