Compound Interest Calculator

Calculate how your investments can grow over time with the power of compound interest. Adjust frequency, contributions, and more.

Calculator Inputs
Initial Investment Principal
$10,000
Annual Interest Rate APR
7%
Investment Length Years
20 years
Compounding Frequency
Tax Rate On Interest
0%
Inflation Rate Annual
3%
Starting Date
Regular Contribution Per Period
$500
Contribution Frequency
Contribution Increase Annual %
0%
Contributions Start
Results
Future Value
$0.00
After 20 years at 7% APR
Total Principal
$10,000
Initial + Contributions
Total Interest
$0
Earnings
Effective Rate
7.23%
APY
Inflation Adj.
$0
Today's Dollars
After Tax Value
$0
Time to Double
10.3 yrs
Rule of 72
Total Contributions
$0
Interest %
0%
of Total
Compounding Frequency Analysis
Annual
Semi-Annual
Quarterly
Monthly
Daily
Continuous
Comparison Analysis
Compounding Future Value Effective Rate Total Interest
Understanding Compound Interest

What is Compound Interest?

Compound interest is interest earned on both the principal amount and the accumulated interest from previous periods. It's often called "interest on interest."

A = P(1 + r/n)^(nt)

Where: A = future value, P = principal, r = annual rate, n = compounding periods per year, t = years

The Power of Compounding

Starting early gives you a significant advantage due to the exponential nature of compound interest. Time is your greatest ally.

Starting at 25 vs 35:
$500/month at 7% for 40 years = $1,317,764
$500/month at 7% for 30 years = $612,936

The 10-year head start more than doubles the result!

Rule of 72

A quick way to estimate how long it takes for an investment to double at a given interest rate:

Years to Double = 72 ÷ Interest Rate

At 8%: 9 years. At 6%: 12 years. At 10%: 7.2 years.

Continuous Compounding

The theoretical limit of compounding frequency, using Euler's number (e ≈ 2.71828):

A = Pe^(rt)

Continuous compounding yields the maximum possible return for a given rate.