Compound Interest Calculator
See how much your money will grow with compound interest and regular contributions.
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The compound interest calculator shows how much your money can grow by combining an initial amount, monthly contributions and reinvested interest. The chart separates what you put in from what the interest earned, which is where the effect of time really shows.
Time matters more than the amount
With 200 a month at 6% a year, compounded monthly and starting from zero:
| Years | Contributed | Interest | Total |
|---|---|---|---|
| 20 | 48,000 | 44,408 | 92,408 |
| 30 | 72,000 | 128,903 | 200,903 |
| 40 | 96,000 | 302,298 | 398,298 |
Going from 20 to 40 years doubles what you contribute but more than quadruples the result. In the final years of a long plan, a single year’s interest is larger than everything you contribute that year.
What the calculator does not know
It assumes the same return every year, and no risky investment behaves like that: a fund can gain 20% one year and lose 15% the next. The result is a reference for comparing scenarios, not a forecast. Nor does it deduct the product’s fees, which come straight off the return: a fund charging 1.5% a year turns 6% into 4.5%, and over 30 years that gap eats a large share of the result.
How to use Compound Interest
- 1
Enter the initial amount
The sum you start with. If you start from zero, enter 0 and rely on the monthly contributions.
- 2
Add the monthly contribution and the interest
How much you will add each month and the annual return you expect, as a percentage.
- 3
Choose the duration and compounding
How many years the money stays invested and how often interest is added to it: monthly, quarterly or yearly.
- 4
Read the result
You get the final balance, how much you put in and how much the interest earned, with a year-by-year chart. Below it is the full table, which you can download as CSV, and a button to copy the result as an image.
Frequently asked questions
What is compound interest?
Interest calculated on the initial amount and also on the interest already accumulated. Each year the interest earns interest of its own, which is why growth speeds up over time instead of being linear.
What is the difference between monthly and yearly compounding?
The more often interest is added, the sooner it starts earning interest of its own. A 6% nominal rate compounded monthly is equivalent to 6.17% effective per year; the calculator always shows you that effective rate. The difference is real, but small next to the one made by the rate itself and the number of years.
Does it account for taxes and inflation?
No. The result is gross: it does not take off the tax you will owe on the gains or the loss of purchasing power. To see what the money will be worth in today's terms, subtract expected inflation from the rate, for example 4% instead of 6% if you expect 2% inflation.
What return should I use?
It depends on the product. A savings account or deposit pays whatever the bank offers at the time. Global stocks have returned around 5% a year above inflation over the last 120 years, but with whole decades far below that. If in doubt, run one cautious figure and one optimistic figure and compare.
Are contributions made at the start or the end of each month?
At the end. In the first month, the contribution goes in after the balance has earned its interest, which is how a monthly savings plan usually works.