What is compound interest?

The Bank of Thailand describes it as interest on interest: deposit 10,000 baht at 5% a year and you have 10,500 after one year; the second year's interest is on 10,500, giving 11,025.

Does compounding more often earn more?

A little. 6% compounded quarterly is an effective 6.14% a year — see the effective annual rate line.

Compound Interest Calculator

Start with this much at this rate: how much after a number of years?

Verified against sourcesLast verified 28 September 2026

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Interest per year

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years

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Made each time interest compounds — with monthly compounding, at the end of every month

Result

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Tested examples

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Formula

Final balance = P × (1 + r/n)^(n × years)
With deposits, add deposit × ((1 + r/n)^(n × years) − 1) ÷ (r/n)
Effective annual rate = (1 + r/n)^n − 1

Assumptions

The rate stays the same throughout
Daily compounding uses 365 days a year
No tax on interest is deducted

Sources

OpenStax (Rice University)
Contemporary Mathematics, §6.4 Compound Interest
accessed 28 September 2026
OpenStax (Rice University)
Contemporary Mathematics, §6.6 Methods of Savings
accessed 28 September 2026
ธนาคารแห่งประเทศไทย
ดอกเบี้ยเงินฝาก
accessed 28 September 2026

Internal reference: reference/14_compound_interest.md

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