📈 Compound Interest Calculator
Project investment growth with compound interest.
About this tool
Compound interest is interest earned on both your original balance and on the interest it's already earned — this calculator projects how a starting amount grows over time at a given annual rate.
If you're modelling regular monthly contributions rather than a single lump sum, the Retirement Savings Calculator handles that version of the same math.
Worked example
Put $5,000 in at 6% annual growth for 15 years and it grows to roughly $11,983 — more than double, without adding another dollar, purely from compounding.
How to use it
- Enter your starting principal.
- Enter the annual interest rate and how many years you plan to grow it.
- Press Calculate to see the projected balance.
Tips
- Even a small rate difference compounds into a large gap over 20-30 years — try comparing two rates side by side.
- Compounding frequency (monthly vs annually) changes the result slightly; this uses annual compounding by default.
- This tool doesn't account for taxes or fees on investment gains.
FAQ
What's the difference between simple and compound interest?
Simple interest is only calculated on the original principal. Compound interest is calculated on principal plus all interest earned so far.
Does this account for regular contributions?
No — for growth with regular monthly deposits, use our Retirement Savings Calculator instead.
Is this good for retirement projections?
It's a reasonable rough estimate, but real returns vary year to year rather than compounding smoothly.
📖 Want the fuller explanation?
See Compound vs Simple Interest for the reasoning behind this calculation, with worked examples.