Compound Interest Calculator
See how your savings grow with compound interest over time.
Inputs
Allowed range: 0 to 100000000
Allowed range: 0 to 1000000
Allowed range: 0 to 100
Allowed range: 1 to 100
Results
How it works
Future value: A = P(1 + r/n)^(nt) + PMT · ((1 + r/n)^(nt) − 1) / (r/n). Compounding frequency matters more the longer your horizon.
Complete guide
Compound interest is what happens when the interest you earn starts earning its own interest. Over a few months it looks small. Over decades it becomes the single most important force in personal finance — Albert Einstein supposedly called it the eighth wonder of the world.
This calculator combines an initial deposit with a recurring monthly contribution and an assumed annual return. The result shows your total balance, how much you actually contributed, and how much came from growth.
Example: $5,000 starting balance + $200/month at a 7% annual return grows to about $123,000 in 20 years. You contributed $53,000 — the other $70,000 is pure compounding. Stretch it to 30 years and the balance more than doubles to ~$278,000.
Two levers matter most: time and contribution rate. Starting 10 years earlier almost always beats trying to invest more later.
Frequently asked questions
- What rate of return should I assume?
- A common long-term assumption for a diversified stock portfolio is 6–8% per year after inflation. Use lower numbers for bond-heavy portfolios and short horizons.
- Does this account for inflation or taxes?
- No. The result is a nominal future value before taxes and inflation. To estimate real purchasing power, subtract about 2–3% from the rate.
- Monthly vs. annual contributions — does it matter?
- Monthly contributions earn slightly more because the money is invested sooner. The difference grows over long periods but is small year to year.
- What if I miss some contributions?
- The future value drops roughly in proportion to what you skipped. Resuming as soon as possible matters more than the exact monthly amount.