📈 Compound Interest Calculator
See how your money grows with compound interest and regular contributions.
How Compound Interest Is Calculated
This calculator applies the standard compound interest formula, adding your monthly contribution at the end of each month and compounding interest at the frequency you select. Compounding more frequently (e.g. daily vs. annually) results in slightly higher growth for the same nominal interest rate.
Frequently Asked Questions
What's a realistic interest rate to use?
Historically, the US stock market (S&P 500) has averaged roughly 7-10% annual returns before
inflation over long periods, though any given year can vary widely and past performance does not
guarantee future results. High-yield savings accounts and CDs typically offer lower, more stable rates.
Does this account for taxes or inflation?
No — this shows nominal growth only. Investment gains may be subject to capital gains tax, and
inflation will reduce the real purchasing power of your final balance.
How does compounding frequency affect my return?
More frequent compounding (daily vs. monthly vs. annually) results in slightly higher growth for the
same nominal interest rate, because interest starts earning its own interest sooner. The difference is
usually small for typical savings rates but grows with higher rates and longer time horizons.
Guide: understanding your result
- Compound interest earns interest on previously earned interest, so growth accelerates over time.
- Time matters as much as the rate: the last decade of a 30-year horizon often adds more than the first two combined.
- Rates here are illustrations, not expected returns — real returns vary and can be negative.
Worked example
Saving $300 a month for 30 years at an illustrative 6% annual rate, compounded monthly, grows to about $301,355. Of that, $108,000 is your own contributions and $193,355 is compound growth.
Contributions vs. compound growth
What $10,000 grows to (no further deposits)
| Time | At 4% | At 6% | At 8% |
|---|---|---|---|
| 5 years | $12,210 | $13,489 | $14,898 |
| 10 years | $14,908 | $18,194 | $22,196 |
| 20 years | $22,226 | $33,102 | $49,268 |
| 30 years | $33,135 | $60,226 | $109,357 |
Compounded monthly. Illustrative rates only.
Rule of 72: years to double
| Annual rate | Rule of 72 | Exact (annual compounding) |
|---|---|---|
| 2% | 36.0 yrs | 35.0 yrs |
| 3% | 24.0 yrs | 23.4 yrs |
| 4% | 18.0 yrs | 17.7 yrs |
| 5% | 14.4 yrs | 14.2 yrs |
| 6% | 12.0 yrs | 11.9 yrs |
| 8% | 9.0 yrs | 9.0 yrs |
| 10% | 7.2 yrs | 7.3 yrs |
Common mistakes to avoid
- Treating an illustrative rate as a guaranteed return.
- Ignoring inflation — use the inflation calculator to see what a future amount is worth today.
Official sources
Examples are calculated live from the same data the calculator uses and are for education only — they are not financial, tax or investment advice.
More Finance calculators
See all →✔ Reviewed by GelirLab Editöryal Ekibi · How we check our calculators