Compound Interest Calculator
See what your money could becomeâand exactly how much comes from your own contributions versus compound growth.
Where the ending balance comes from
Year-by-year growth
| Year | Contributed | Growth earned | Ending balance |
|---|
This is a planning estimate, not a forecast. It assumes a constant annual return, monthly compounding and end-of-month contributions. Taxes, fees and market volatility are not included.
How compound interest works
Compound growth means returns can earn additional returns over time. CalcBunny applies the annual return as an equivalent monthly rate and compounds the starting balance and each monthly contribution over the remaining months.
With $10,000 invested today, $500 added each month, a 7% annual return and 20 years, the ending balance is roughly $286,000. About $130,000 comes from the money you contributed and the rest comes from investment growth.
Why contributions matter so much
Compounding gets the attention, but consistent contributions usually do much of the heavy liftingâespecially early on. Increasing the monthly contribution can sometimes have a bigger effect than assuming a slightly higher return.
What this calculator assumes
The calculator uses a steady annual return converted to a monthly rate. Real investments do not grow smoothly, so use the result for scenario planning rather than as a guaranteed outcome.
Frequently asked questions
Are monthly contributions included?
Yes. Each monthly contribution is assumed to be made at the end of the month and then compounds for the months that follow.
Is the annual return the same as an APY?
Not necessarily. This calculator treats the number as an annual investment return and converts it to a monthly rate. Bank products may quote APY using specific compounding conventions.
Does this include inflation?
No. The result is shown in future nominal dollars. Inflation would reduce the purchasing power of that future balance.
Does it include taxes or fees?
No. Taxes, fund expense ratios, advisory fees and trading costs are excluded.
Can the return be negative?
Yes, for scenario testing down to -99%, although long-term investment planning usually uses a positive expected return.