How it works
Compound interest is interest earned on both your original principal and on interest you've already earned. This calculator combines a lump-sum starting balance with regular monthly contributions, compounded at the frequency you choose, using the standard future-value-with-contributions formula. It reports the future value of your savings, how much of that total came from your own contributions versus interest earned, and shows the year-by-year growth so you can see how compounding accelerates over time. Use it to compare different contribution amounts, rates, or timelines when planning retirement or savings goals.
Compound Interest Calculator
See how your savings grow with regular contributions and compounding interest.
FAQ
What's the difference between simple and compound interest?
Simple interest is calculated only on your original principal. Compound interest is calculated on your principal plus any interest already earned, so your balance grows faster over time.
Does compounding frequency matter much?
More frequent compounding (monthly vs. annually) produces a slightly higher return at the same stated rate, but the effect is usually small compared to the impact of rate, time, and contribution size.
What if I want to model a lump sum with no contributions?
Set the monthly contribution to 0 — the calculator will show pure compound growth on your starting principal alone.
Is the interest rate guaranteed?
No — this tool assumes a constant annual rate for simplicity. Real investments fluctuate year to year; use this as a planning estimate, not a guarantee.
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