PayCalcMoney and everyday maths
Compound Interest Calculator
Enter your starting amount, a monthly contribution, an expected annual return and a time period. Interest is compounded monthly in this calculator.
How it works
Future value = P × (1 + r/12)^(12t) + PMT × [((1 + r/12)^(12t) − 1) ÷ (r/12)], where P is the starting amount, PMT the monthly contribution, r the annual rate and t the years.
Worked example
$10,000 growing at 5% a year for 10 years with $100 a month added reaches about $31,998: $22,000 contributed and roughly $9,998 of interest.
Frequently asked questions
Is this a prediction?
No. It is maths using the constant rate you enter. Real investments move up and down and rarely grow at a steady rate.
Why does starting early matter?
Interest earns interest. The same monthly amount contributed over 20 years instead of 10 produces far more than double the interest, because earlier contributions compound for longer.
This calculator gives an estimate for planning. It does not account for taxes or deductions unless stated. See the disclaimer.