Compound Interest Calculator
Work out how much your money grows with compound interest. Enter a starting amount, an annual rate and how long you invest, then choose how often interest compounds — daily, monthly, quarterly or yearly. Add an optional regular contribution to model a savings plan, and see your future value, total interest and a full year-by-year growth table. Everything is calculated instantly in your browser, with no sign-up.
The yearly rate before compounding, e.g. 3 for a 3% p.a. deposit.
How long the money stays invested (up to 100 years).
An amount you add every period. Leave blank for a lump sum only.
Your results will appear here
Enter a starting amount and a period to see your compound growth.
Future value The total balance at the end, including principal, contributions and all compounded interest.
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Total invested Your own money in: the starting amount plus every contribution.
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Total interest Future value minus everything you put in — the interest earned.
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Effective annual rate The true yearly return once compounding is applied: (1 + r/n)^n − 1.
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After 15% withholding tax
| Interest before tax | — |
| Withholding tax (15%) | — |
| Net interest after tax | — |
| Future value after tax | — |
Banks withhold 15% tax on deposit interest. Personal savings-account interest is exempt if your total savings interest stays under ฿20,000 per year. This estimate taxes all interest; your real result may differ.
Year-by-year growth
| Year | Contributions | Interest | Balance |
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Contributions and interest are shown cumulatively. Balance = starting amount + contributions + interest.
Compounding frequency compared
| Compounding | Future value | Interest | Effective rate |
|---|
Same inputs, different compounding intervals. More frequent compounding earns slightly more.
How to use
- Enter your starting amount (principal) and the annual interest rate.
- Set the investment period in years and pick the compounding frequency.
- Optionally add a regular contribution and choose how often you pay it in.
- Tick the 15% withholding tax option to see interest after Thai deposit tax.
- Read the future value, total interest and year-by-year table, then copy or download the results.
Features
- Daily, monthly, quarterly or yearly compounding
- Optional regular contributions at the start or end of each period
- Future value, total invested, interest earned and effective annual rate (EAR)
- Year-by-year growth table you can download as CSV
- Compounding-frequency comparison so you can see the effect of each interval
- 15% Thai withholding tax option with the ฿20,000 savings exemption note