Investing €100 a month: how much you will have in 10, 20 and 30 years

One of the ideas that holds people back from investing is thinking you need a lot of money. You don't: almost every Spanish broker lets you contribute to an index fund with very little each month. The interesting question is a different one: how far does a small amount go if you keep it up for many years?

The table: monthly contribution × years

Assuming a 6% annual return — reasonable for a mostly global-equity portfolio over the long run, though never guaranteed — and contributions at the start of each month:

Per month	10 years	20 years	30 years
€50	€8,235	€23,218	€50,477
€100	€16,470	€46,435	€100,954
€200	€32,940	€92,870	€201,908
€300	€49,410	€139,305	€302,861
€500	€82,349	€232,176	€504,769

Look at the €100 row. In 10 years you have put in €12,000 and have €16,470: modest growth. In 30 years you have put in €36,000 and have €100,954: almost two thirds of the total is return, not your own money. That jump between the early and late years is compound interest in its purest form.

Starting earlier beats contributing more

Compare two people who contribute exactly the same, €48,000:

• Ana invests €100 a month for 40 years and ends up with about €200,145.
• Bruno invests €200 a month for 20 years and ends up with about €92,870.

Same total effort, more than double the result. Time is the variable that weighs most, and the only one you cannot get back. If today you can only manage €50 or €100, start with that: raising the contribution later is easy; recovering lost years is impossible.

What if the return is different?

The 6% is an assumption. With €100/month for 30 years, the result by return would be:

• 3% (very conservative portfolio): €58,419
• 5%: €83,573
• 7%: €122,709
• 8%: €150,030

Two points of return, over 30 years, almost double the result. That is why the share of equities matters so much and, above all, what you pay in fees: every tenth of a point of TER comes straight out of that return.

What the table does not say

• Inflation. The €100,954 in 30 years' time, with 2.5% inflation, is worth about €47,724 today. Still more than double what you contributed in real terms, but worth knowing. We explain it in inflation and real return.
• Taxes. As long as you do not sell, you pay nothing. When you sell, the gain is taxed as savings income: with €200/month for 20 years, about €9,300 of the €92,870. If you withdraw gradually instead of all at once, you pay less and later. Details in index fund taxation.
• Volatility. The table rises in a straight line; reality does not. There will be years when your portfolio is worth less than you put in. Contributing every month no matter what (DCA) is exactly what makes you buy cheap during those drops.

How to start with €100 a month

1. Build a cushion first. An emergency fund keeps you from having to sell at the worst moment.
2. Pick a cheap global index fund. An MSCI World or similar fund with a TER under 0.3% is enough to start.
3. Automate it. Schedule a recurring contribution for the day after payday. What never lands in your current account is not missed.
4. Raise the contribution with your salary. Every pay rise is a chance to increase the €100 without noticing.
5. Don't check every day. With small contributions and a long horizon, the best strategy is almost always to do nothing.

In short

• €100 a month for 30 years at 6% is about €100,954, having contributed €36,000.
• Starting ten or twenty years earlier matters more than doubling the contribution.
• Account for inflation and taxes so you do not overestimate the result.
• What matters is not the starting amount, but starting and being consistent.

Educational content, not financial advice. The figures assume a constant annual return, with no fees or taxes except where stated; real returns vary and can be negative.