Compound Interest
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See what a balance grows to, with regular deposits and any compounding.
- Put in what you are starting with, the rate and the years
- Add a regular deposit if you make one
- Check the effective annual rate to compare two offers
You end with
Year
| Year | Paid in | Interest | Balance |
|---|
Arithmetic only — no tax, inflation or fees, and not advice.
About this tool
A starting amount, a rate, how often interest is added, and how long for. Optionally something paid in every period. Out comes the balance year by year, split between what you put in and what the interest did. How often interest compounds matters more than people expect. 5% compounded monthly is not 5% a year — it is 5.116%, and over decades that gap is not small. So the compounding frequency is an input rather than an assumption, and the effective annual rate comes back alongside the result: that is the figure that makes two different offers comparable. There is also a switch for whether deposits land at the start or the end of each period. Money paid in at the end earns nothing that period, so paying at the start earns one extra period of interest across the whole run. It is a real difference and a real choice, so it is not made quietly on your behalf. This is arithmetic, not a forecast. It knows nothing about tax, inflation, fees or what any investment will actually do, and none of those are small. A projection that looks like a promise is the one dishonest thing a calculator like this can do, so: it is a sum, and the sum assumes the rate holds exactly.
Frequently asked questions
Why is 5% monthly not the same as 5% a year?
Because each month's interest earns interest of its own for the rest of the year. 5% nominal compounded monthly works out to 5.116% actually earned — the effective annual rate. It is the only figure that lets you compare an account paying monthly against one paying yearly.
Should deposits go at the start or the end of the period?
Whichever is true for you. Money paid in at the end earns nothing that period, so starting-of-period deposits earn one extra period of interest over the whole run. Salary-day transfers usually land at the start; the difference is small monthly and visible over decades.
Does this account for tax or inflation?
No, and both matter. Tax takes a share of the interest in most countries, and inflation reduces what the final number is worth. Treat the result as the arithmetic of the rate you typed, not as what you will really have.
Is this investment advice?
No. It is a sum. It has no idea what any investment will actually return, and a rate you type in is an assumption rather than a prediction. For anything that matters, talk to somebody licensed to advise you.
How is the growth actually calculated?
Step by step, one compounding period at a time, rather than with a closed-form formula. That is what makes the yearly table possible and keeps the deposit timing honest — and the tests check it against the textbook formula in the cases where the formula applies.
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