What effective rate is a 3% flat rate?

About 5.6–5.7% a year over 2–5 years. The Bank of Thailand's rough rule is to multiply by 1.8, but the exact figure depends on the term — choose Flat rate and read the effective-rate line.

Is there a cap on car-loan interest in Thailand?

Yes. For personal-use hire-purchase contracts made from 10 January 2023, the effective rate may not exceed 10% a year for new cars, 15% for used cars and 23% for motorcycles (Contract Committee announcement B.E. 2565).

Why doesn't my contract match this figure?

Lenders often round the payment up to a whole number and charge interest by the actual days in each month. In the Bank of Thailand's example the formula gives 2,142.31 baht but the lender collects 2,150 baht, with a smaller last payment.

Loan Payment Calculator

Monthly instalment and total interest, flat rate or reducing balance

Verified + our stated conventionLast verified 28 September 2026

Your numbers

Interest method

Amount borrowed

THB

Interest per year

Number of monthly payments

months

Result

Enter your numbers on the left. The result appears here instantly.Enter your numbers above. The result appears here instantly.

Tested examples

Every example below is an automated test. Click one to try it.

Formula

Flat rate: total interest = amount × yearly rate × years, spread evenly over the payments
Reducing balance: payment = amount × i ÷ (1 − (1 + i)^−n), with i = yearly rate ÷ 12

Assumptions

One equal payment a month
Fees, insurance and the down payment are not included; enter only the amount financed
A flat rate's effective rate is the reducing-balance rate giving the same payment (monthly rate × 12)

Sources

ธนาคารแห่งประเทศไทย
ดอกเบี้ยเงินกู้แบบเงินต้นคงที่
accessed 28 September 2026
ธนาคารแห่งประเทศไทย
ดอกเบี้ยเงินกู้แบบลดต้นลดดอก
accessed 28 September 2026
ธนาคารแห่งประเทศไทย
เช่าซื้อรถ
accessed 28 September 2026
สำนักงานคณะกรรมการคุ้มครองผู้บริโภค (สคบ.)
ประกาศคณะกรรมการว่าด้วยสัญญา เรื่อง ให้ธุรกิจให้เช่าซื้อรถยนต์และรถจักรยานยนต์เป็นธุรกิจที่ควบคุมสัญญา พ.ศ. 2565
accessed 28 September 2026
OpenStax (Rice University)
Contemporary Mathematics, §6.8 The Basics of Loans
accessed 28 September 2026
OpenStax (Rice University)
Principles of Finance, §8.3 Loan Amortization
accessed 28 September 2026

Internal reference: reference/16_loan_payment.md

FAQ

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