Compound Interest Calculator

Free compound interest calculator — see how your investments grow over time with different contribution schedules and compounding frequencies. No affiliate bias.

Future Value
$0
Total Contributions
$0
Interest Earned
$0
$
$0$500K
$
$0$5K
%
0%20%
years
1 yr40 yrs

Growth Over Time

Formula Used

FV = P × (1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) - 1) / (r/n)] Where: FV = Future value P = Initial principal r = Annual interest rate (decimal) n = Compounding periods per year t = Time in years PMT = Regular contribution per compounding period For monthly contributions with monthly compounding: FV = P × (1 + r/12)^(12t) + PMT × [((1 + r/12)^(12t) - 1) / (r/12)]

How This Compound Interest Calculator Works

Compound interest is the most powerful force in finance. Our calculator uses the standard future value formula, accounting for both your initial investment and regular contributions.

Why Compounding Frequency Matters

  • More frequent compounding = slightly more growth: $10K at 7% for 20 years: annual = $38,697, daily = $40,552
  • The real magic is time: Starting 5 years earlier with the same contributions can mean 40%+ more at retirement
  • Consistent contributions win: $500/month for 20 years at 7% = ~$260K, vs only $38K from the initial $10K alone

The Rule of 72

Divide 72 by your rate to estimate doubling time. At 7%: 72/7 ≈ 10.3 years to double. At 10%: 7.2 years. This works for any rate.

Frequently Asked Questions

What is compound interest?
Compound interest is interest earned on both your original deposit and on previously earned interest. It's what makes long-term investing so powerful — your money earns money on its earnings.
How often should interest compound?
More frequent compounding = slightly more growth. Daily compounding earns marginally more than monthly, which earns more than annually. The real game-changer is time — start early.
What is the Rule of 72?
Divide 72 by your interest rate to estimate how many years it takes to double your money. At 7%: 72/7 ≈ 10.3 years to double. At 10%: 72/10 ≈ 7.2 years.