Compound Interest Calculator — Free
Project a balance when principal and periodic additions compound at a constant stated rate. Contributions repeat at the selected compounding frequency, making this a mathematical scenario rather than a market forecast.
- Runs in your browser
- Nothing is uploaded
- No signup; device limits apply
Numbers stay on your device. Nothing is sent to a server.
Added at each compounding period. Leave at 0 for a lump sum only.
How to use this tool
Enter principal, annual rate, years and compounds per year, then an addition per period. Quarterly compounding also means quarterly additions here, so do not mistake that field for an always-monthly deposit.
Results and examples
With 1000 principal, 10% annual compounding and no additions for two years, the balance is 1210. The model separates 1000 contributed from 210 interest, and monetary results are displayed in USD.
Limitations
- Taxes, fees and varying period returns are excluded.
- Additions occur at period end; actual products can use different daily calculations and rounding.
Fields
| Field | Guidance and constraints |
|---|---|
| Principal | Accepted range: 0–100000000 · Input step: 100 |
| Annual interest rate | Accepted range: 0–50 · Input step: 0.1 |
| Years | Accepted range: 0.5–60 · Input step: 0.5 |
| Compounds per year | Annually / Semiannually / Quarterly / Monthly / Daily |
| Contribution each period | Added at each compounding period. Leave at 0 for a lump sum only. · Accepted range: 0–1000000 · Input step: 10 |
Data handling
Processing stays in the current browser tab; the site does not upload tool input for the calculation itself.
Sources
Frequently asked questions
Why does 1000 become 1210 after two years?
With 1000 principal, 10% annual compounding and no additions for two years, the balance is 1210. The model separates 1000 contributed from 210 interest, and monetary results are displayed in USD.
Are contributions always monthly?
Taxes, fees and varying period returns are excluded. Additions occur at period end; actual products can use different daily calculations and rounding.
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