Compound Interest
Calculate future value with compound interest and optional monthly contributions. Shows year-by-year growth, total contributions, and total interest earned — useful for savings planning.
Future value
$144,572.72
Total contributed
$58,000.00
Interest earned
$86,572.72
How to use the compound interest
Set your starting amount, annual interest rate, time horizon, monthly contribution, and how often interest compounds. Future value, total contributions, and interest earned compute live.
Formula & explanation
FV of principal: A = P(1 + r/n)^(nt). FV of monthly contributions: c × ((1 + r/12)ᵗ⁾¹² − 1) / (r/12). Total = both, summed.
Examples
10k starting, 7%, 20 yr, 200/mo contribution = ~144k future value, ~58k contributed, ~86k interest.
Frequently asked questions
- Why is the interest so much larger than contributions?
- Compounding — interest earns interest. The longer the time horizon, the more dramatic the effect.
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