Compound
Interest
See how your investments grow over time with compounding. Enter your principal, contributions, and rate to see the full picture.
Investment Details
Balance Growth Over Time
Growth Milestones
Year-by-Year Growth
| Year | Balance | Contributions Added | Interest Earned |
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About this calculator
Compound interest is calculated on both the original principal and the interest that has already accumulated. The standard formula is A = P(1 + r/n)^(nt), where P is principal, r is the annual rate, n is compounding periods per year, and t is time in years. More frequent compounding (monthly vs. annually) produces slightly more growth because interest is reinvested sooner.
A useful mental shortcut is the Rule of 72: divide 72 by the annual interest rate to estimate how many years it takes to double your money. At a 6% annual return, money doubles roughly every 12 years. At 9%, every 8 years. The rule is an approximation, but accurate enough for planning purposes.