Compound Interest Calculator
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Explore a savings scenario using a starting balance, monthly contributions and an assumed annual rate. See deposits and calculated interest separately.
Preparing your tool…
A visual example
See which growth comes from interest on interest
Keep contributions at zero to see the compounding effect on its own.
Use explicit assumptions Setting Value Initial amount 1,000 Monthly contribution 0 Annual rate 10% Duration 2 years Use explicit assumptions
Start with 1,000, add nothing monthly, and assume an effective annual rate of 10% for two years.
The second year's base is larger
The first year adds 100. In year two, 10% of 1,100 adds 110, giving 1,210.
The extra 10 in year two comes from interest on the first year's interest.
Illustrative example. This is a mathematical scenario with a constant assumed rate, not an investment forecast. Fees, taxes and inflation are not included.
How to use it
- Set a starting balance, monthly contribution, effective annual rate and duration.
- Choose whether contributions arrive at the start or end of each month.
- Review the projected balance, contributions and annual table.
1,000 with 10% effective annual growth and no deposits becomes 1,100 after one year.
Details & limits
Up to 100 years with monthly contributions. Effective annual rate converted to a monthly rate. No taxes, fees or inflation.
What assumptions does the projection make?
The monthly rate is (1 + annual rate ÷ 100)^(1/12) − 1. Contributions happen every month, consistently at its beginning or end. All amounts use your chosen unit or currency consistently; no exchange conversion occurs. Rates are constant; taxes, fees and inflation are excluded. This is a hypothetical projection, not a guaranteed return or personal financial advice.