Compound Interest Calculator
Project the long-term growth of an investment with regular contributions. Tweak interest, frequency and time horizon — see how compounding does the heavy lifting.
Inputs
Growth — Contributions vs Interest
Frequently Asked Questions
How does compound interest work?
Compound interest earns returns on both your original principal and the interest already accumulated. Over time this creates exponential rather than linear growth, so the longer your money compounds, the larger the share of the final balance that comes from interest rather than contributions.
How often should interest compound?
More frequent compounding (monthly or daily) yields slightly more than annual compounding at the same nominal rate, but the difference is small compared with the rate itself and how long you stay invested. The calculator lets you compare annual, monthly and daily frequencies.
Do monthly contributions or the interest rate matter more?
Early on, your contributions dominate the balance; over long horizons, the interest rate and time in the market matter more as compounding takes over. Both levers are shown separately in the chart so you can see the crossover.
What annual return is realistic?
Historically, broad stock-market indices have returned roughly 6–8% per year after inflation over multi-decade periods, while cash and bonds return less. Past performance is not a guarantee — this tool is for projection only and is not financial advice.
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