Goal and time horizon
It's not the investment that determines the time frame, it's the time frame that determines the investment. Money you'll need in two years doesn't belong in volatile assets.
Every euro you set aside has a deadline. The car repair might come next year, the kitchen renovation in five, retirement in thirty. Something different fits each of those.
Rule of thumb: money for the next three years stays safe and available. Money for three to ten years can be mixed. Money you won't need for over ten years can handle volatility.
The reason is simple. Prices fluctuate, and the shorter the time frame, the bigger the risk that you need exactly what you put in right when it's at a low point.
Write your goals down, with an amount and a year. That list is worth more than any stock tip, because it answers the one question that's actually about you: what is this for.
The reasoning lies in how returns are distributed over time. Expected return grows linearly with holding period, while standard deviation grows only with its square root. As a result, the probability of a negative outcome falls as the holding period lengthens, even though the absolute range of possible final values keeps widening.
It's important to read this effect correctly. It doesn't mean stocks become safe over time. Historically there have been ten-year periods and longer with a negative real result, for instance after 1929 and after 2000. The claim is only that a long horizon lowers the probability of a forced sale at a low point, and gives compounding time to work.
In practice, this leads to allocating by time buckets rather than building a single portfolio. Every goal gets an amount, a date, and a matching type of investment. This approach also answers, as a side effect, how large your equity allocation should be: it follows from the sum of your goals with a long horizon, not from a general recommendation.
Summary
- Set the date first, then the type of investment.
- Under three years, money doesn't belong in volatile assets.
- A long horizon doesn't make stocks safe, but it lowers the pressure to sell.
Did you get it?
Why does the probability of a loss fall with a longer holding period?
Because expected return grows linearly with time, while volatility only grows with the square root of time.
Does that mean stocks become safe after ten years?
No. There have historically been decades with a negative real result. A long horizon only lowers the pressure to sell at a low.
What determines your equity allocation?
The sum of your goals with a long time horizon, not a general recommendation.
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