There is a conversation that repeats itself with minimal variation. Someone arrives at forty looking at their first serious savings, does the maths on what they would have accumulated if they had started investing at thirty, and finds the gap profoundly unfair. It is not unfair: it is simply what time does to money when it is allowed to work.
The most costly investment mistake is almost never choosing the wrong fund, paying commissions 0.3% higher than necessary, or selling during a moment of panic. The most costly mistake, in most cases, is not starting at all. Or starting ten years late.
Why time matters more than the amount
Compound interest is not a difficult concept, but its long-term results are counterintuitive because humans think in linear terms while compound interest grows exponentially.
When you invest money and earn a return, that return is added to the initial capital. The following year, you earn a return on the initial capital plus the accumulated return. That process, repeated over decades, produces curves that appear insignificant at the start and become steep at the end.
The key is not the amount invested each month, though that matters. The key is how much time that process has to work. Ten additional years at the beginning of your investment life have a multiplier effect you can never replicate by saving more aggressively ten years later.
This is not a debatable principle or an opinion: it is arithmetic. What varies is the assumed annual return and each person’s circumstances, but the direction of the argument is always the same.
What ten years of difference actually do
Numbers illustrate better than any conceptual explanation. Consider two people investing in an index fund with an average annual return of 7%, reinvesting dividends, with monthly contributions of €200.
Ana starts at 25 and maintains that monthly contribution until 65. She has been investing for forty years. Her total cash contribution is €96,000. With compound returns, her portfolio at 65 reaches approximately €525,000.
Luis starts at 35 — ten years later — and maintains exactly the same monthly contribution of €200 until 65. He has been investing for thirty years. His total cash contribution is €72,000. With the same return, his portfolio at 65 reaches approximately €243,000.
The difference is more than €280,000. Ana has contributed only €24,000 more than Luis over her lifetime, yet her final wealth is more than double. Those initial ten years are not a tenth of the total: they account for more than half the outcome.
What Luis contributed over thirty years, with exactly the same discipline and rigour, could not compensate for the ten-year head start Ana had at the beginning. The gap between starting at 25 versus 35 is arithmetically impossible to close simply by saving more.
The reasons we use to wait
The reasons for not starting to invest are familiar because we all use them at some point. They are worth examining directly.
“I don’t have enough yet.” The feeling that you need to reach a significant minimum amount before starting is understandable but wrong. The world’s best index funds can be accessed from €50 or €100 per month. There is more time to accumulate a larger capital by investing than by saving while waiting for that capital.
“I’ll wait until markets fall.” This strategy has a technical name: market timing. Decades of research and practice demonstrate that investors who try to enter at the best moment achieve worse results than those who invest regularly regardless of timing. Nobody knows when markets will fall or by how much. And while you wait, time passes.
“I need to understand how it works better first.” Continuous learning about investing is valuable, but it is not a prerequisite for starting. A low-cost global index fund is a vehicle that requires no sophisticated knowledge to be appropriate for most long-term investors. You can learn while investing, which is in fact the most effective way to learn.
“Now isn’t the time, with everything that’s happening.” Something is always happening. Markets have risen over the long term despite wars, financial crises, pandemics and recessions. Uncertainty does not disappear: it is the permanent condition of any era.
How much you need to start
The real answer to this question is: less than you think.
Index funds from major asset managers like Vanguard, BlackRock and their European equivalents can be accessed from very low minimums through major brokers. There are platforms that allow automatic monthly contributions from €50 with no transaction fees.
The argument that you should complete your emergency fund before investing is reasonable: there is no sense in taking market risk with money you might need in the next six months. But once that basic buffer is covered — typically three to six months of expenses in an accessible, risk-free account — there is no reason to wait.
The most effective approach for most people is automation: setting up an automatic monthly contribution the day after being paid, so the money moves before it can be spent. This requires no active discipline — which is limited for everyone — just a system that works on its own.
The most honest argument
There is no perfect moment to start investing. The best time was yesterday; the second best is today.
This may sound like a motivational slogan, but there is a mathematical reason behind it. Every year that passes without investing is a year of compound returns that will never occur. It cannot be recovered by increasing later contributions: the numbers simply do not add up, as the comparison between Ana and Luis demonstrates.
The alternative to the risk of investing is not safety: it is the different risk of inflation eroding the purchasing power of idle money, and the opportunity cost of years of compound growth that did not happen.
Long-term investing guarantees nothing, but historical data shows that periods of twenty or more years in diversified global markets have produced positive returns in virtually every recorded case. The real uncertainty lies in the short term, which is precisely where money you will not need for several years should not be.
The question is not whether the timing is right. The question is how many more years you want to wait.
