First, a buffer
Money in shares can fall sharply in a single year, so it should be money you will not need soon. Build an emergency fund first. The UK's MoneyHelper suggests three to six months of essential outgoings in an instant-access savings account as a rule of thumb.[1] High-interest debt, such as credit card debt, usually costs more than the stock market returns, so it normally makes sense to repay that first.
Then an amount you can keep up
How long you keep saving matters more than how much you start with. Choose an amount you will not miss, and set up an automatic transfer for the day after payday. Raise it when your income rises. A popular rule of thumb, the 50/30/20 budget, puts about 20% of take-home pay towards savings and debt repayment. Treat it as a starting point, not a requirement.
What different amounts become
The table assumes a 9% annual return every year – roughly the 20-year average of a global index fund (MSCI World) in USD, before fees. Real returns vary from year to year and can be negative.
| Per month | After 10 years | After 25 years | You put in (25 years) |
|---|---|---|---|
| 100 EUR | 19,000 EUR | 106,000 EUR | 30,000 EUR |
| 250 EUR | 47,000 EUR | 264,000 EUR | 75,000 EUR |
| 350 EUR | 66,000 EUR | 370,000 EUR | 105,000 EUR |
| 500 EUR | 95,000 EUR | 529,000 EUR | 150,000 EUR |
Starting early beats saving more
At the same 9%, 175 EUR a month for 35 years grows to about 471,000 EUR. 350 EUR a month for 25 years grows to about 370,000 EUR. The first saver puts in 73,500 EUR, the second 105,000 EUR. Ten extra years do more than doubling the amount. That is the snowball effect.
Common questions
Is it worth investing a small amount?
Yes. A small amount started early can end up larger than a bigger amount started late, and it builds the habit. Check that your platform does not charge a fixed fee per purchase that eats a large share of a small deposit.
Should I pay off debt before investing?
High-interest debt usually comes first, because its interest rate is normally higher than the return you can expect from the stock market. For low-interest debt such as many mortgages the answer depends on your situation.
Sources & further reading
We cite independent authorities so you can verify everything yourself. Last reviewed 15 Sept 2026.