A compound interest calculator shows how money grows when earnings are reinvested. Enter the starting principal, annual interest rate, number of years and how often interest compounds to see the final balance, the total interest earned, and a year-by-year table of the growth. A vivid demo of why starting early matters.
Investment details
Growth
Year-by-year growth
| Year | Start balance | Interest earned | End balance |
|---|
Illustrative projection. Real returns vary; fees and taxes are not included.
How is compound interest calculated?
With A = P(1 + r/n)^(nt): principal times one plus the periodic rate, raised to the total number of periods. $10,000 at 7% compounded monthly for 10 years grows to about $20,097.
More frequent compounding means slightly more growth, because interest starts earning interest sooner. Compare frequencies above to see the difference.
What is the difference between compound and simple interest?
Simple interest pays only on the original principal; compound interest pays on principal plus accumulated interest. Over long periods, compounding wins by a wide margin.
At 7% for 30 years, $10,000 earns $21,000 simple but about $76,123 compounded monthly: the gap is the snowball effect.
Why does starting early matter so much?
Because compounding is exponential, extra years at the start beat larger contributions later. Money invested at 25 has 15 more compounding years than money invested at 40.
The year-by-year table above shows growth accelerating: later years earn far more interest than early ones.
Frequently asked questions
What compounding frequencies are supported?
Annually, semiannually, quarterly, monthly and daily. Daily compounding gives the highest balance for the same nominal rate.
Does it include regular contributions?
No. This models a single lump-sum principal. Regular monthly contributions would grow the balance further.
Are taxes and fees included?
No. Real investment returns are reduced by fees, and gains are usually taxable. Treat results as an illustration, not a prediction.
What is the effective annual rate shown?
The true yearly growth rate after compounding frequency is accounted for. Monthly compounding at 7% nominal gives about 7.23% effective.
Is my data uploaded anywhere?
No. All projections run in your browser with JavaScript. Nothing leaves your device.