Compound interest is interest earned on your interest, and over long periods it does most of the heavy lifting in savings and investing. This free compound interest calculator shows how a starting balance plus regular monthly contributions could grow over time. Enter your initial deposit, how much you'll add each month, an expected annual interest rate or return, the number of years and how often interest compounds (daily, monthly, quarterly or yearly). You'll see the final balance, how much of it came from your own contributions and how much from interest, and a year-by-year table that makes the "snowball" visible: in later years, the interest earned each year can overtake what you put in. It's useful for comparing high-yield savings accounts, ISAs, TFSAs, 401(k)s, super or any other account, and for seeing what difference starting five years earlier makes. Choose US dollars, pounds, euros, Canadian or Australian dollars. Be realistic about the rate: savings rates change, and investment returns are never guaranteed and can be negative. The calculator ignores tax, fees and inflation, all of which reduce real-world growth. It runs fully in your browser.
Calculate compound growth
Year by year
Contributions are added at the end of each month. Ignores tax, fees and inflation. Not financial advice.
How to use the compound interest calculator
- Enter your starting amount and monthly contribution.
- Enter a realistic rate and the number of years.
- Choose the compounding frequency from your account terms.
- Read the year-by-year table to see when interest overtakes contributions.
The formula
A = P(1 + r/n)nt for a lump sum. With monthly contributions we calculate month by month, using an effective monthly rate of (1 + r/n)n/12 − 1.
FAQ
What is the Rule of 72?
Divide 72 by the annual rate to estimate how many years it takes to double your money. At 6%, that’s about 12 years.
Does compounding frequency matter much?
A little. At 5%, monthly compounding gives an effective rate of about 5.12% versus 5% yearly. Contributions and time matter far more.
Can I model investments like an index fund?
You can enter an expected average return, but real returns vary year to year and can be negative. Treat the result as an illustration, not a forecast.
Does it include inflation?
No. To see roughly what the money would be worth in today’s terms, subtract an expected inflation rate from the interest rate.
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