Compound Interest Calculator
Calculate how an investment grows over time with compound interest and regular contributions, with a year-by-year breakdown.
About Compound Interest Calculator
Compound interest means earning returns on your returns. Interest earned in one period is added to the balance, and the next period's interest is calculated on that larger amount. Over long horizons this is the difference between a modest sum and a large one, and the effect is genuinely hard to intuit without seeing the numbers.
Enter a starting amount, a rate, a time period and any regular contribution, and the calculator shows the final balance broken into what you put in and what the interest earned. The year-by-year table makes the shape of the curve visible: growth is unremarkable early on and accelerates sharply later, which is precisely why starting early matters more than contributing more.
Compounding frequency is adjustable from annual to daily. The difference between them is smaller than most people expect — moving from annual to daily compounding at the same rate changes the outcome by a fraction of a percent, while changing the rate itself changes everything.
How to use it
- 1Enter your initial deposit and the annual interest rate.
- 2Set how many years the money will stay invested.
- 3Add a regular monthly or annual contribution if you make one.
- 4Review the total and the year-by-year breakdown.
Common uses
- Projecting how a savings account or investment might grow
- Comparing the effect of starting to save five years earlier
- Seeing how much a small monthly contribution adds over decades
- Understanding how much of a final balance is interest rather than deposits
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original amount, so it grows in a straight line. Compound interest is calculated on the balance including previously earned interest, so it curves upward. Over a year the difference is small; over thirty years it is enormous.
How much does compounding frequency matter?
Less than people assume. Going from annual to monthly compounding at the same rate adds a fraction of a percent to the outcome. The rate and the time period dominate — frequency is a rounding detail by comparison.
Does this account for inflation or tax?
No. The figures are nominal. Real purchasing power grows more slowly than the numbers suggest, and returns are usually taxed. For a rough real-terms view, subtract expected inflation from the rate before entering it.
Is this financial advice?
No. It is arithmetic. It shows what a given rate produces over a given period, and assumes a constant return that no real investment provides. Talk to a qualified adviser before making decisions with your money.