Lump sum and contributions together
A starting amount and optional monthly contributions are compounded together, so you can model a real savings plan rather than a one-off deposit.
Compound Interest Calculator
Future value of a lump sum plus monthly contributions, compounded your way.
- Input
- No upload needed — instant
- Privacy
- Nothing is uploaded
- Cost
- Free · no sign-up · no watermark
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Overview
About the Compound Interest Calculator
Project how savings grow with compound interest from a starting amount, rate, years, compounding frequency and monthly contributions, showing future value and interest earned.
Compound interest is why starting early beats saving more later. This calculator projects a starting amount plus optional monthly contributions forward at a steady annual rate, compounding as often as you like, and shows the future value alongside how much of it is growth rather than deposits.
The maths
A lump sum grows by
FV = P × (1 + r/n)^(n·t)with r the annual rate, n the compounding periods per year and t the years. Monthly contributions are added as an ordinary annuity, compounded monthly, and summed with the grown lump.
Why time dominates
Because the exponent is time, an extra decade at 7% roughly doubles the outcome, while an extra percent adds far less. The growth-multiple figure makes this tangible: it shows how many times over your contributions the final balance is.
Private and precise
Every figure is worked out in your browser with standard financial formulas. Nothing you type is uploaded, stored or sent anywhere.
Step by step
How to use the Compound Interest Calculator
Enter the amount you are investing today and choose a currency.
Set the expected annual return and how many years it stays invested.
Choose the compounding frequency and add any monthly contribution.
Read the future value, the interest earned and the growth multiple.
Why use it
Benefits and common use cases
What this tool is good for, and what it deliberately does not try to do.
Pick the compounding frequency
Compound annually, semi-annually, quarterly, monthly or daily to match how a real account credits interest.
Growth versus deposits
The result is split into what you put in and what growth added, with a growth multiple that makes the effect of time obvious.
Questions
Frequently asked questions
Short, honest answers about quality, limits and privacy.
What is compound interest in simple terms?
It is interest earned on interest. Each period you earn a percentage of the whole balance — your original money plus all the growth so far — so the balance climbs faster every year.
Does compounding frequency matter?
Yes, but only slightly. Daily compounding gives a little more than monthly, which gives a little more than annual, for the same nominal rate. The rate and the time invested matter far more.
Is the return guaranteed?
No. This projects growth at a steady rate you choose. Real investments vary year to year, so treat the result as an illustration, not a promise.