What if you invested €100 a month in the S&P 500?

Putting €100 into the S&P 500 on the first trading day of every month from August 2021 to August 2026 would have turned €6,100 of your own money into €9,777 — +60.3% on what you put in. The same total invested all at once on the first day would have been €11,411.

What those numbers mean

The schedule made 61 contributions of €100 across August 2021 to August 2026, so €6,100 of your own money went in over the period rather than on day one — which is why the percentage is a return on contributions and not a share price move. Here the lump sum finished ahead, which is the usual result — money invested on day one spends the longest compounding, and markets rise more often than they fall. Along the way the position fell 22% from its high at the worst point. That figure is the one people underestimate, and it is the reason a plan you can actually keep beats a better plan you abandon.

Why the S&P 500 specifically

This is the version of the question most people should be asking. A single company can go to zero; an index quietly replaces its failures. The number below is the one to compare every other page on this list against — if a stock did not beat this, the extra risk bought nothing.

the S&P 500 is the 500 largest US companies, held through the SPY exchange-traded fund. Change the ticker in the calculator above to run the same schedule on anything else — the numbers on this page are just one setting of it.

What this calculation does and doesn’t include

Contributions land on the first trading day of each month at the closing price. Dividends are included and treated as reinvested. Taxes are ignored, and so are the fees your broker charges on a small monthly purchase — on a €100 contribution a flat commission is a real drag that this does not model. The window is the free five-year one, which matters more than it sounds: five years is one market cycle at most, and a schedule that started five years ago is not the same experiment as one that started in 2007.

Above all, this is one company over one stretch of history that already happened. It cannot tell you what the next five years hold, and picking the ticker with the best number on this list is choosing with hindsight — which is the one advantage you will never have in advance.

The same question, other companies

Want to compare strategies rather than companies? The full backtester runs rule-based setups — moving-average crossovers, breakouts, mean reversion — against buy & hold on the same prices.