Compound Interest Calculator
See how an investment grows when interest earns interest. Adjust the values and results update instantly.
Future value: $0.00
Total contributions: $0.00
Total interest earned: $0.00
How compound interest works
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. The formula for a lump sum is:
A = P (1 + r/n)^(nt)
- P = principal (initial amount)
- r = annual interest rate (decimal)
- n = compounding frequency per year
- t = time in years
- A = final amount
When you add regular monthly contributions, each contribution also compounds from the month it is added. That is why starting early and contributing consistently has such a large effect over long periods.
Why it matters for discipline
The math rewards consistency, not intensity. A modest monthly contribution sustained for decades outperforms occasional large deposits. Use this calculator to set a concrete target, then pair it with a budget (see our savings goal calculator) so the contribution becomes automatic.