Compound Interest Calculator
Free compound interest calculator. See what a starting amount and regular deposits grow into, choose how often interest compounds, and find the year your earnings overtake everything you put in. No currency is assumed.
No currency is shown on purpose: the numbers come out in the same unit you type them in.
| Year | Total you put in | Total earned | Balance |
|---|
What it does
Compound interest is interest that earns interest. Put money in, let it sit, and each round of interest joins the pile that the next round is calculated on. The effect is slow at first and then stops being slow: the line that looks almost flat for years bends upward, and the moment it does is when what you earned passes what you deposited. Two things drive it — how long the money stays, and how often the interest is added — and of the two, time does far more of the work than rate.
How to use it
- Enter the amount you start with, the annual rate and how many years the money stays.
- Add a regular deposit if you make one, and say how often interest is added.
- Read the final balance, how much of it you put in, and how much the money earned by itself.
The arithmetic runs in your browser. Nothing you type is sent anywhere and nothing is stored, so you can use these with real numbers.
Frequently asked questions
What does the compounding frequency actually change?
How often interest is added to the balance, and so how soon it starts earning on itself. At 12% a year, compounding once a year really gives you 12%; compounding monthly gives 12.68%, because each month's interest starts working the next month. That second number is the effective annual rate this page shows, and it is the one to compare between two offers.
My deposits and the compounding are on different schedules. What happens?
Money earns from the moment it is in the account, but interest is only added on the compounding dates. A deposit made halfway through a period earns for half the period, at simple interest, and joins the compounding from the next date on. Most calculators quietly assume your deposits match the compounding schedule and give a higher number than you will actually see.
Does it account for inflation or tax?
No. This is the arithmetic of the account, nothing else. Real returns are smaller: inflation eats part of the growth, and most places tax the interest. A useful rough check is to run it again with the rate minus the inflation you expect — the result is then in today's money.
Why is there no currency?
Because the calculation is identical in every currency, and picking one would make the page wrong for all the others. Type the amounts in the currency you use, and read the answer in the same unit.
Wikipedia — Compound interest
Wikipedia — Effective interest rate
Wikipedia — Future value
Wikipedia — Rule of 72