Compounding Calculator
Project how a starting balance grows under a fixed per-period rate, with optional recurring contributions, using standard compound-interest arithmetic.
Calculator
Match the rate's period (e.g. months).
Added at the end of each period (optional).
Formula
- Principal FV = Principal × (1 + r) ^ n
- Contributions FV = Contribution × ((1 + r) ^ n − 1) ÷ r
- Future value = Principal FV + Contributions FV (r = rate ÷ 100)
How it works
Compounding describes growth that builds on previous growth: each period's return is earned on the prior balance plus everything earned so far. Over many periods this produces the familiar curved trajectory.
This calculator uses a constant per-period rate and treats any recurring contribution as an ordinary annuity (added at the end of each period). It is a deterministic arithmetic model — real returns vary, can be negative, and are never guaranteed.
Use it to understand the mechanics of compounding and the effect of contributions and time. It is an educational illustration, not a projection of any actual outcome and not financial advice.
Example use cases
Pure principal growth
$1,000 at 10% per period for 2 periods → $1,210 ($210 of growth).
Regular contributions
Start at $0, add $100 per period at 10% for 3 periods → $331 from $300 contributed.
Frequently asked questions
Is the rate annual or per period?+
Per period. If you compound monthly, enter the monthly rate and the number of months. Mixing an annual rate with monthly periods will give incorrect results.
Does this guarantee returns?+
No. It assumes a fixed rate you choose for illustration. Actual returns fluctuate and can be negative; this tool makes no prediction and offers no advice.