€100 a month for 30 years: what it actually grows to
Put €100 a month away for 30 years at a 5% annual return, and you end up with €83,226. Of that, only €36,000 came out of your own pocket — the remaining €47,226 is interest your money earned on its own. That gap between what you paid in and what you end up with is the entire case for starting early and staying consistent.
The scenario
- €100 deposited every month
- 30 years, no interruptions
- No starting lump sum — you begin at zero
- Interest compounds monthly
- Deposits made at the end of each month
The result at three rates
| Annual rate | Final amount | Paid in | Interest earned |
|---|---|---|---|
| 3% | €58,274 | €36,000 | €22,274 |
| 5% | €83,226 | €36,000 | €47,226 |
| 7% | €121,997 | €36,000 | €85,997 |
In every case you’ve handed over the same €36,000 — that’s fixed by the €100 monthly amount and the 30-year term. What changes with the rate is how hard that money works while it sits there.
What this example is really showing
At 3%, interest is a useful top-up: it adds about 62% on top of what you paid in. At 5%, interest overtakes your own contributions — you end up with more money earned than money saved. At 7%, interest does more than double the heavy lifting, contributing €85,997 against your €36,000.
This is what compound interest looks like when it’s given decades to work. Each month’s interest gets added to the balance and starts earning interest itself, so growth accelerates rather than staying flat. The early deposits matter most, because they’re the ones with the most time to compound — a euro saved in year one has 30 years to grow, while a euro saved in year 29 has barely any.
The other lesson is about scale. €100 a month feels small, and it’s easy to dismiss a monthly habit as second-best to putting away a lump sum when you happen to have one. But run through decades of compounding, that €100 a month isn’t rounding-error money. It’s tens of thousands of euro, and at higher rates, the interest alone outstrips everything you contributed. Small, consistent amounts are a wealth-building mechanism in their own right, not a consolation prize for people who can’t save more.
Try your own numbers
If your monthly amount, timeframe, or expected rate is different, run it through the compound interest calculator to see your own figures.
Assumes a constant annual rate and deposits at the end of each month; it ignores fees, tax and inflation, all of which would reduce the real-world result.
Questions people ask
Is it worth saving small amounts?
Yes, if there's time for it to work. €100 a month at 5% for 30 years becomes €83,226, of which €47,226 is interest. Small amounts aren't small once they've had decades to compound.