Compound Interest Calculator
See how savings grow with compound interest and regular deposits — any compounding frequency, with a year-by-year growth table.
For information and education only — not financial advice. Results are estimates based on the numbers you enter; check important decisions with a qualified professional.
How to use
- 1Enter the starting amount, interest rate and number of years.
- 2Add a regular monthly deposit and pick how often interest compounds.
How it's calculated
A = P(1 + r/m)^(m·t) for the starting amount, plus deposits D grown as D × ((1 + i)^k − 1) ÷ i, where i is the effective rate per deposit period and k the number of deposits.
Frequently asked questions
What is compound interest?
Interest earned on both your original money and the interest already added. Over long periods it grows much faster than simple interest.
Does compounding frequency matter much?
A little. At 5% a year, monthly compounding gives an effective 5.12% versus 5% with annual compounding. Time and rate matter far more.
What is the rule of 72?
Divide 72 by the annual rate to estimate the years to double your money — about 10 years at 7.2%, or 14.4 years at 5%.