The question everyone asks with a windfall
An inheritance, a bonus, a house-sale surplus: do you invest it all at once, or feed it in monthly “to be safe”? The maths has a clear answer and your nervous system has a different one — and both matter, because the strategy you abandon in a crash is worse than the imperfect one you keep.
What the evidence says
Markets go up more often than they go down — roughly two years in three, plus dividends the whole time. So money on the sidelines waiting to be drip-fed is, on average, missing returns. Studies across decades and countries (Vanguard’s is the best known) find investing a lump sum immediately beats drip-feeding it in about two-thirds of historical periods, typically by 1–2% over the first year. Time in the market beats timing the market, and drip-feeding a lump sum is timing the market in slow motion — just with the decision spread over twelve smaller flinches.
The corollary people miss: if you hold a lump sum in cash because investing it “all at once feels risky”, you have already made an all-in decision — 100% cash.
Where the drip-feed genuinely earns its keep
Regular investing from salary isn’t a strategy choice at all — the money arrives monthly, so you invest it monthly. That’s pound-cost averaging by default, and it’s excellent: automatic, emotionless, and it buys more units when prices are low. Set up the standing order and let it run through every headline.
And for a windfall, the honest case for drip-feeding is psychological, not mathematical. If investing £200,000 on a Tuesday means you’d panic-sell when it’s worth £160,000 by Christmas, then spreading it over 6–12 months is a fair insurance premium: you sacrifice a percent or so of expected return to buy a strategy you’ll actually stick with. Decide the schedule in advance, automate it, and finish it — the failure mode is pausing “until things calm down”, which is how a 12-month plan becomes permanent cash.
If a lump sum feels unbearable at your current allocation, the real message may be that the allocation is too aggressive — see the diversified portfolio guide. A portfolio you can hold through a 30% fall beats a braver one you can’t.
Staying invested: the part that actually determines your returns
Crashes are not a malfunction of the market — they are the market, and the reason equities pay more than cash. A global portfolio falls 10%+ most years at some point, 20%+ every few years, and occasionally 40%+. Every one of these, so far, has been temporary; the damage that proved permanent was done by people selling in the middle.
The behavioural traps have names, and knowing them helps:
- Loss aversion — losses hurt roughly twice as much as gains please, so a normal down year feels like an emergency.
- Recency bias — after a fall, more falling feels inevitable; after a rise, so does more rising. Both feelings are noise.
- Action bias — in a crisis, doing something feels responsible. In investing, activity is a cost, not a virtue.
The practical defences are structural, not willpower: automate contributions so buying continues through the dip; hold enough cash (see the emergency fund guide) that you’re never a forced seller; check the portfolio annually, not daily; and write down, now, in calm weather, what you’ll do in a 30% crash — which should be “nothing, keep buying”.
The one-line summary
Invest windfalls promptly if your nerves allow it, on a fixed automatic schedule over months if they don’t — and remember the returns you keep are decided less by the entry date than by refusing to sell in the storms that follow.
Related guides & tools
- Building a diversified portfolio — an allocation you can hold through a 30% fall
- Emergency funds and where to keep cash — the buffer that stops forced selling
- Low-cost index fund investing — what the monthly standing order should buy
- ISA investing — wrap the windfall before investing it
- Financial Planner — model the windfall against your longer-term plan
Last reviewed: July 2026.