Compound Interest Calculator

Enter your starting amount, monthly contribution, expected annual return, and time horizon to project how compounding grows your money. Adjust the compounding frequency to see its effect.

Your numbers

Adjust the sliders or type exact values.

Initial investment

$0$250,000

Monthly contribution

$0$5,000

Annual interest rate

0%20%

Years to grow

yrs

1 yrs50 yrs

Compounding frequency

Future value in 20 years

$144,573

Assumes a constant annual return and contributions made at each compounding period.

Total contributions: $58,000
Total interest earned: $86,573
Interest share of balance: 59.9%
Growth multiple: 2.49×

Balance growth over time

ContributionsInterest earned

Estimates are for informational purposes only and do not constitute financial advice.

The compound interest formula

The first term compounds your initial deposit; the second term compounds the stream of regular contributions. Together they describe how most savings and investment accounts grow.

A = P(1 + r/n)ⁿᵗ + PMT × [((1 + r/n)ⁿᵗ − 1) ÷ (r/n)]

A: Future value of the investment
P: Initial principal (starting amount)
r: Annual interest rate (as a decimal)
n: Compounding periods per year
t: Number of years
PMT: Contribution made each compounding period

Example: $10,000 plus $200 a month for 20 years

1
Start with P = $10,000, add PMT = $200 per month, earn r = 7% compounded monthly (n = 12), for t = 20 years.
2
The monthly rate is 7% ÷ 12 ≈ 0.5833% (0.005833), and there are 12 × 20 = 240 compounding periods.
3
Initial deposit grows to: 10,000 × (1.005833)²⁴⁰ ≈ $40,387.
4
Contributions grow to: 200 × [((1.005833)²⁴⁰ − 1) ÷ 0.005833] ≈ $104,185.
5
Total future value ≈ $144,572 — you contributed $58,000, so compounding added about $86,572.