Compound Interest Calculator
Grow a lump sum plus monthly contributions with any compounding frequency.
How to use the Compound Interest Calculator
- Enter your figures in the fields above — results update instantly as you type.
- Choose your currency symbol (the maths is the same in any currency).
- Use Share result to save a link that reloads your exact inputs, or Print for your records.
- Compare scenarios by changing one input at a time and noting how the main result moves.
Formula
A = P(1 + r/k)^(k·t) (lump sum) Contributions are added monthly and grown at the equivalent monthly rate.Worked example
10,000 at 7% compounded annually for 30 years becomes about 76,122.55. Compounded monthly it becomes about 81,164.97. Adding 300 a month (108,000 of deposits) grows to roughly 447,000 combined.
Frequently asked questions
What return should I assume?
Use a conservative real (after-inflation) return for planning; historical equity returns vary widely by period and market.
Does compounding frequency matter much?
It matters less than rate and time. Moving from annual to monthly compounding adds a few percent over decades.
What is the Rule of 72?
Divide 72 by the annual rate to estimate years to double: at 8%, about 9 years.
Learn more
Assumptions & limits
Results are estimates based on the inputs you provide and the formula shown, rounded for display. They do not account for every fee, tax rule or market condition. This tool is educational and is not financial, tax or legal advice — confirm important decisions with a qualified professional.
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