Growth Over Time
Total Value
Principal + Contributions
Interest Earned
| Year | Balance | Contributions | Interest |
|---|
About this tool
Compound Interest Calculator
Compound Interest Calculator projects what a starting balance grows to over time, with regular monthly contributions, a choice of compounding frequency, a growth chart and a year-by-year breakdown.
How to use it
- Enter your starting principal and annual interest rate.
- Set the time period and how often interest compounds: annually, quarterly, monthly or daily.
- Add a monthly contribution if you plan to keep paying in.
- Read the projection and the year-by-year table.
Why compounding pulls away from simple interest
Simple interest pays only on the original principal. Compound interest pays on the principal plus everything it has already earned, so each period starts from a larger base. That is why the curve bends upward instead of running straight.
Compounding frequency matters less than people expect. Going from annual to monthly compounding at the same rate adds a fraction of a percent. What actually dominates the result is the rate, the time, and how much you keep adding.
Worked example
Using the values the calculator loads with:
- Starting principal$10,000
- Annual rate7%
- Monthly contribution$200
- Time period20 years
Result: About $137,000. Of that, $58,000 is money you put in and roughly $79,000 is growth. The growth overtakes the contributions somewhere around year twelve.
When it helps
- Projecting a retirement or index fund balance over a long horizon.
- Seeing what raising a monthly contribution by $50 does over twenty years.
- Comparing two savings rates over the same period.
- Understanding why starting five years earlier beats contributing more later.
Common mistakes
- Using a nominal return and forgetting inflation. A 7% return with 3% inflation is about 4% in real buying power.
- Assuming a steady rate. Real markets do not deliver 7% every year, and the order of good and bad years matters once you start withdrawing.
- Confusing APR with APY. APY already includes compounding, APR does not.
What this tool handles
- This is a projection tool, not financial advice. Past returns do not predict future ones.
