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Financial Calculators

Compound Interest Calculator

See how money grows when interest earns interest. Set the compounding frequency and, if you like, a regular monthly contribution, then follow the balance year by year.

$
% p.a.
years
$
Future value$54,713.58
Total contributed
$34,000.00
Interest earned
$20,713.58
Effective annual rate
7.229%
  • Contributions 62.1%
  • Interest 37.9%
Step-by-step working
  1. Initial amount grows as P(1 + r/n)^(n·t) = $10,000.00 × (1 + 0.07/12)^(12 × 10) = $20,096.61
  2. Monthly additions of $200.00 grow at the equivalent monthly rate 0.583333%: FV = PMT × ((1 + i)ᵐ − 1) ÷ i = $34,616.96
  3. Total = $54,713.58

Contributions are added at the end of each month. Taxes and fees are not included.

Growth by year

YearContributedInterest to dateBalance
Year 1$12,400.00$801.42$13,201.42
Year 2$14,800.00$1,834.27$16,634.27
Year 3$17,200.00$3,115.28$20,315.28
Year 4$19,600.00$4,662.39$24,262.39
Year 5$22,000.00$6,494.83$28,494.83
Year 6$24,400.00$8,633.24$33,033.24
Year 7$26,800.00$11,099.74$37,899.74
Year 8$29,200.00$13,918.03$43,118.03
Year 9$31,600.00$17,113.55$48,713.55
Year 10$34,000.00$20,713.58$54,713.58

How to use the Compound Interest Calculator

  1. Enter your starting amount and the annual interest rate.
  2. Enter how long you will keep the money invested.
  3. Choose how often interest is compounded and, optionally, a monthly top-up.
  4. Press Calculate.

Formula

A = P(1 + r/n)n·t + PMT × ((1 + i)m − 1) ÷ i

P = initial amount, r = annual rate, n = compounding periods per year, t = years, PMT = monthly contribution, m = months, i = (1 + r/n)n/12 − 1 is the equivalent monthly rate.

Examples

  • 10,000 at 7% compounded monthly for 10 years grows to ≈ 20,096.61 without additions.
  • Adding 200 a month brings the total to ≈ 54,713, of which 34,000 is contributions.

Frequently asked questions

How much difference does compounding frequency make?

Less than many people think. At 7%, yearly compounding gives an effective 7.00% and daily gives 7.25%. The rate and the time invested matter far more.

What is the rule of 72?

Divide 72 by the annual rate to estimate the years needed to double your money. At 8%, about 9 years.

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