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calcthai.com · Compound Interest Calculator
Money & tax
Compound Interest Calculator
Project the future value of your savings with compound interest, from a starting sum plus a regular monthly contribution, with a year-by-year breakdown.
Balance year by year
| Year | Deposited that year | Return earned | Balance at year end |
|---|---|---|---|
| Year 1 | 36,000 | 1,348 | 47,348 |
| Year 2 | 36,000 | 3,259 | 86,607 |
| Year 3 | 36,000 | 5,268 | 127,875 |
| Year 4 | 36,000 | 7,379 | 171,254 |
| Year 5 | 36,000 | 9,598 | 216,852 |
| Year 6 | 36,000 | 11,931 | 264,783 |
| Year 7 | 36,000 | 14,383 | 315,166 |
| Year 8 | 36,000 | 16,961 | 368,127 |
| Year 9 | 36,000 | 19,671 | 423,798 |
| Year 10 | 36,000 | 22,519 | 482,317 |
Ask about this page
The AI assistant answers only questions about the calculator on this page.
Compound interest means returns are added back to the balance, and the next period earns a return on that larger amount. For the first few years the effect looks negligible. It becomes obvious as time passes, because the money that grew on its own starts producing more than the money you keep adding. The year-by-year table above shows exactly where that crossover happens for your numbers.
How it works
The formula. This tool calculates two parts and adds them. The first is the initial sum compounding forward. The second is the stream of monthly contributions, each of which has a different amount of time to grow — the first month’s deposit compounds for the entire period, the last month’s barely at all.
It compounds monthly, which matches how most Thai deposit accounts and mutual funds actually work.
Why time matters more than the amount. Compare two people, both earning 7% a year. The first saves 3,000 baht a month for 30 years, putting in 1,080,000 baht of their own money. The second saves 9,000 baht a month for 10 years, putting in exactly the same 1,080,000. The first ends up with about 2.3 times as much, because their money had far longer to compound.
The lesson is that starting early beats saving heavily. If you can only save a small amount right now, start anyway rather than waiting until you can save more.
Choosing a realistic rate. The figure you enter should reflect risk you would actually take. Thai fixed deposits pay around 1-2% a year, which barely keeps pace with inflation. Bond funds are around 2-3%. Long-run equity investing has historically averaged 7-10%, but with years of heavy losses along the way.
An important caveat. This projection assumes an identical return every single year, which no real investment delivers. Anything with meaningful return fluctuates constantly, and past performance does not guarantee future results. The figures also ignore inflation, tax and management fees, all of which eat into what you actually end up with. Treat this as an illustration for planning, not a promise.
Frequently asked questions
How is compound interest different from simple interest?
Simple interest is always calculated on the original amount. Compound interest is calculated on the original amount plus everything earned so far. Deposit 100,000 baht at 5% for 10 years: simple interest gives 5,000 a year for a total of 50,000, while compounding gives about 64,700 — nearly 15,000 more from the same deposit at the same rate. The longer the period, the wider that gap.
How much should I save each month?
A common guideline is at least 10-20% of income, but consistency matters more than the number. Saving 1,000 baht every month beats saving 5,000 sporadically. Set up an automatic transfer for the day your salary arrives, so it does not depend on willpower each month.
Why does it grow so slowly in the early years?
Because the balance is still small, so the return on it is small too. In that phase almost all the growth comes from your own deposits rather than from returns. The interesting moment is when the annual return starts to exceed everything you contribute in a year. Look at the year-by-year table to see when that happens — that is the point where the money begins working harder than you do.
How much can I rely on this projection?
Use it to shape a plan, not as a promise. It assumes a constant return every year, which real investments never deliver, and it ignores inflation, tax and fees. One million baht twenty years from now will buy considerably less than one million baht buys today.
Sources
- Bank of Thailand — Financial Consumer Protection Center
- Stock Exchange of Thailand — investor education
Rates last verified 25 Aug 2026