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Compound Interest Calculator

See how money grows over time with compound interest. Choose your compounding frequency, add monthly contributions, and compare compound vs simple interest on a graph.

Growth Over Time

1246810YearsCompoundSimple

Parameters

$
%
years
$/mo

Results

Final Amount
$17,175.24
Total Interest Earned
$4,175.24
Total Contributions
$13,000.00
Doubling Time (Rule of 72)
14.4 years
Simple Interest (comparison)
$13,500.00

Step-by-Step Calculation

1. Compound interest formula

A=P(1+rn)ntA = P\left(1 + \frac{r}{n}\right)^{nt}

2. Substitute values

A=1000(1+0.0512)12⋅10A = 1000\left(1 + \frac{0.05}{12}\right)^{12 \cdot 10}

3. Calculate rate per period

rn=0.0512=0.00416667\frac{r}{n} = \frac{0.05}{12} = 0.00416667

4. Final amount (principal only)

A=$17175.24A = \$17175.24

5. Doubling time (Rule of 72)

tdouble≈725=14.4 yearst_{\text{double}} \approx \frac{72}{5} = 14.4 \text{ years}

Year-by-Year Breakdown

YearBalanceInterest EarnedTotal Contributions
1$2,279.05$79.05$2,200.00
2$3,623.53$144.49$3,400.00
3$5,036.81$213.27$4,600.00
4$6,522.38$285.58$5,800.00
5$8,083.97$361.58$7,000.00
6$9,725.44$441.48$8,200.00
7$11,450.90$525.46$9,400.00
8$13,264.64$613.74$10,600.00
9$15,171.17$706.53$11,800.00
10$17,175.24$804.07$13,000.00

Reference Guide

Compound Interest Formula

Compound interest earns interest on previous interest, causing exponential growth.

A=P(1+rn)ntA = P\left(1 + \frac{r}{n}\right)^{nt}

P is principal, r is annual rate, n is compounding frequency, and t is time in years.

Continuous Compounding

When compounding happens infinitely often, the formula uses the natural exponential.

A=PertA = Pe^{rt}

Rule of 72

A quick estimate for how long it takes to double your money. Divide 72 by the annual interest rate.

tdouble≈72r%t_{\text{double}} \approx \frac{72}{r\%}

Compound vs Simple

Simple interest grows linearly. Compound interest grows exponentially. The difference becomes dramatic over long time periods, which is why starting to save early matters so much.