Compound Interest Calculator
See what a starting amount plus a monthly contribution grows into, and how much of it is interest.
Free No signup Runs in your browser — nothing uploaded
€
€
%
y
- Final balance
- € 39,291.50
- Total you put in
- € 29,000.00
- Interest earned
- € 10,291.50
- Same money under a mattress
- € 29,000.00
- Worth in today's money at 2% inflation
- € 32,232.72
What it does
Compound Interest Calculator shows the whole calculation, not just the answer: every intermediate figure is on screen, so you can check it against your own numbers instead of trusting a single output box.
When you need it
Quoting, invoicing, or checking someone else's arithmetic — the moments where being roughly right costs money, and where the formula is easy to get subtly backwards.
Limits and caveats
Figures are unrounded until the final display, so results will not always match a calculation that rounded at each step. This is a working tool, not tax or financial advice, and local rules may differ. Everything happens in your browser, so the file never leaves your device.
How to use the Compound Interest Calculator
- Enter your numbers.
- Results update as you type.
- No rounding surprises — the maths is shown in full.
Frequently asked questions
- Why does it include a monthly contribution?
- Because compounding a lump sum on its own answers a question almost nobody has. What people want to know is what happens if they add to it every month, which is a different formula added on top.
- What is the 'today's money' figure?
- The same balance discounted at 2% a year. €100,000 in twenty years buys what about €67,000 buys now, and a growth calculator that hides that is flattering you.
- Is the return guaranteed?
- No. This is arithmetic on a rate you chose, not a forecast — a real investment does not return the same percentage every year, and the order of the good and bad years changes the outcome.