Compound Interest Calculator
See how a lump sum grows when interest earns interest.
Balance year by year
For information only. Results are estimates based on the numbers you enter and a constant rate. They are not financial, tax or investment advice — real returns, fees, taxes and lender terms vary. Speak to a qualified adviser before making financial decisions.
How it works
- Enter the starting amount and annual interest rate.
- Choose how many years and how often interest compounds.
- See the final balance, interest earned and effective annual rate, with a year-by-year table.
Frequently asked questions
What is the compound interest formula?
A = P × (1 + r ÷ n)^(n × t), where P is the starting amount, r the annual rate as a decimal, n the number of compounding periods per year and t the number of years.
Does compounding frequency matter much?
More frequent compounding earns slightly more. At 12% per year, annual compounding gives 12%, while monthly compounding gives an effective 12.68% per year.
What is the effective annual rate?
It is the actual yearly growth once compounding is included, which makes offers with different compounding schedules easy to compare.
Can I add regular deposits?
This calculator is for a single lump sum. Use the Investment Calculator to include monthly contributions.
The power of compounding
With compound interest, each period's interest is added to the balance and earns interest itself. Over long periods this snowball effect becomes dramatic — which is why starting to save early matters so much.
The rule of 72
A quick way to estimate doubling time: divide 72 by the annual rate. At 6% money doubles in about 12 years; at 9%, about 8 years. Try it in the calculator to see how close the rule gets.