Compound Interest Calculator
See how a starting balance and regular contributions compound — and exactly when growth overtakes what you put in.
Your numbers
Result
Year-by-year breakdown
| Year | Contributed | Interest | Balance |
|---|
Compound interest is interest earning interest. The longer your money stays invested, the more the growth itself starts to generate growth — which is why time in the market tends to matter more than the size of any single deposit.
The two engines of growth
Your final balance comes from two sources: what you put in, and what the returns generate. Early on, contributions dominate. Given enough time, the interest line overtakes them entirely — the chart makes the crossover point obvious. The “interest share of total” figure shows how much of your ending balance you never had to deposit.
The cost of waiting
Push the time horizon out by a few years and the future value jumps far more than the extra contributions alone would suggest. That gap is the compounding you forfeit by starting late, and it is the single strongest argument for investing early and consistently.
Questions, answered
What return rate should I use?
Use a rate that reflects your investments. Broad stock-market averages have historically landed in the high single digits before inflation, while cash and bonds are lower. Lower the rate for a conservative estimate; this tool does not predict any specific market.
Does it account for inflation?
No. Results are in today's nominal currency. To see purchasing power, lower the return rate by your expected inflation rate — that gives an approximate inflation-adjusted, or real, growth figure.
Monthly vs annual compounding — does it matter?
A little. More frequent compounding produces slightly higher results for the same nominal rate. This calculator compounds monthly, which matches how most investment accounts accrue.
Why does the contribution increase option help?
Raising contributions as your income grows keeps your saving rate steady in real terms and meaningfully lifts the final balance. Even a small yearly step-up compounds over decades.