Compound Interest Calculator
See how savings grow with compound interest and monthly contributions.
How to use Compound Interest Calculator
- Enter what you start with and what you add each month.
- Set the yearly rate, years and compounding frequency.
- Read the future value and the yearly table of contributions versus interest.
How it works
Compound interest earns interest on previous interest. Without contributions the formula is A = P × (1 + r/n)^(n·t), where r is the yearly rate as a decimal, n the number of compounding periods per year and t the years. With monthly contributions, each deposit is grown using the equivalent monthly rate (1 + r/n)^(n/12) − 1, so any compounding frequency can be combined with monthly saving.
The effective annual rate shows the true yearly growth after compounding. For investments, the rate is an assumed average; real returns vary from year to year and can be negative.
Example
10,000 at 5% compounded monthly for 10 years grows to 16,470.09 (10,000 × (1 + 0.05/12)^120).
Frequently asked questions
How often should interest compound?
More frequent compounding earns slightly more: 5% compounded monthly is an effective 5.12% a year; daily is 5.13%.
What rate should I use for investments?
Use a conservative long-term assumption, and remember inflation and fees reduce real growth. This calculator does not predict returns.
Does it include taxes or inflation?
No. Subtract expected tax and inflation from the rate for a rough real (after-inflation) estimate.
What is the rule of 72?
A shortcut: 72 ÷ rate ≈ years to double. At 7% money doubles in about 10.3 years; the exact answer is ln 2 ÷ ln 1.07 ≈ 10.2.
Limitations
- Assumes a constant rate and regular contributions.
- Excludes taxes, fees and inflation.
- For information only, not financial advice.
Last reviewed November 9, 2026. How we build and test tools.