All at once or bit by bit
Putting money in all at once or spreading it over months is really a question of time in the market, not timing it.
The study
Vanguard compared investing a lump sum immediately against spreading the same amount over 12 months, across decades of US, UK and Australian data. The lump sum came out ahead in roughly two tries out of three.
Why all at once usually comes out ahead
Markets rise more years than they fall, so money sitting in cash waiting to be spread out is usually missing a rise. Each euro invested earlier simply gets more time to compound.
A worked example
Put €1,200 in on day one of a year the market rises 10% and it becomes €1,320. Spread the same €1,200 evenly over 12 months while the market climbs steadily, and the later instalments buy at higher prices, so the year ends with less than €1,320.
When spreading it out comes out ahead
If prices fall for a while after you start, spreading it out buys some of those later months cheaper, and it is also far easier to live with: no single bad week carries your whole decision.
The real choice
This is a trade between a slightly better expected result (all at once) and a steadier ride while you invest it (spread out). Neither is "wrong"; a large windfall is where the choice matters most.
Key takeaways
- Lump sum beats spreading it out more often than not, because markets rise more than they fall.
- Spreading it out buys cheaper if prices fall after you start, and feels calmer either way.
- The decision matters most for a one-off sum, not for a monthly saving habit.