Car Loans in Thailand: What Is the True Interest Rate? Don't Be Fooled by Flat Rate
What Is Flat Rate?
When a dealer or bank quotes "1.79%" or "2.5%" per year, that is a Flat Rate — calculated on the original full loan amount throughout the entire contract, not on the remaining principal that decreases each month.
Why Flat Rate Is Misleading
Example: Borrow 800,000 THB for a car at 2.5% Flat Rate over 60 months.
- Total interest = 800,000 × 2.5% × 5 years = 100,000 THB
- Total repayment = 900,000 THB
- Monthly installment = 900,000 ÷ 60 = 15,000 THB/month
But calculated as an Effective Rate (APR) — the true interest against the declining balance — that same 2.5% Flat Rate equals approximately 4.7% APR.
Converting Flat Rate to Effective Rate
Effective Rate ≈ Flat Rate × 1.8–1.9 (approximate for 4–5 year loans)
- Flat Rate 1.5% → Effective Rate ≈ 2.7–2.85%
- Flat Rate 2.5% → Effective Rate ≈ 4.5–4.75%
- Flat Rate 3.0% → Effective Rate ≈ 5.4–5.7%
How to Compare Car Loan Offers
- Ask for the APR (Annual Percentage Rate) from every bank — not just the Flat Rate figure
- Compare using the Effective Rate, not the Flat Rate
- Calculate total installments over the full contract term and compare the total amount paid
- A larger down payment significantly reduces total interest
How Much Down Payment Is Appropriate?
Financial experts recommend a down payment of at least 20–30% of the car's price, keeping monthly installments below 15% of your monthly income — a level that protects both savings and other expenses.
Source: Bank of Thailand (bot.or.th) — Automotive hire-purchase loan supervision guidelines