Should I invest a lump sum all at once or spread it out over time?
Historically, investing a lump sum at once beat spreading it out about two-thirds of the time. Spreading it reduces the regret of bad timing, and it beats leaving the money in cash.
If the money is meant for the long term and your target mix is settled, investing it at once has usually done better. Vanguard’s 2023 study found that a lump sum invested immediately beat the same sum fed in over a few months roughly two-thirds of the time. Spreading it out is not a mistake — it buys you protection from the regret of investing the day before a fall — but it has an expected cost, and the longer you spread it, the higher that cost.
Why investing at once usually wins
Markets have risen more often than they have fallen, so money waiting in cash usually misses growth. Over 1976–2022, Vanguard found US shares beat 3-month Treasury bills 76% of the time. Cost averaging means part of your money sits in cash for months, and that is where the shortfall comes from.
What the study measured
- Global shares (MSCI World), rolling one-year periods from 1976 to 2022, with similar results in the United States, the United Kingdom, Australia, Canada and the European Union.
- A lump sum against splitting it into three equal parts invested a month apart.
- Lump sum beat cost averaging 68% of the time. Cost averaging beat staying in cash 69% of the time.
- Allowing interest on the cash still waiting, the lump sum still won 65% of the time in an all-equity portfolio. Higher interest on cash narrows the gap.
- Spreading over a longer period widened the gap further.
When spreading it out makes sense
Vanguard’s own conclusion is that cost averaging may suit someone with a very high aversion to losses who would otherwise leave the lump sum in cash. If a fall in the first month would make you abandon the plan altogether, a few months of phasing is a reasonable price for staying invested. The important thing is to decide the schedule before you start — for example, equal parts on the first of each month for three or six months — so the news does not decide it for you.
Common mistakes
- Waiting for a dip with no rule. Without a fixed schedule, “I will invest after the next fall” can mean holding cash for years.
- Asking the wrong question first. If you are unsure whether a lump sum belongs 80% in shares or 40%, settle the mix before the timing. A sum invested in a mix you are comfortable with makes the timing question much smaller.
- Investing money you need soon. An emergency fund and anything due within a few years should not be in shares at any speed.
What would change the answer
A short horizon, a high and secure rate on cash, or a portfolio mostly in bonds all shrink the advantage of investing at once. A long horizon and a mostly-equity mix enlarge it.
In your plan
Nivritee’s projection grows everything counted in your savings at the plan’s return assumption; it does not model money waiting in cash to be invested. If you hold a large sum in a current account for a long time, the projection is more optimistic than your money is. Enter a lump sum where it actually sits today, and if it is arriving later, record it as money coming in.
Sources
- Cost averaging: Invest now or temporarily hold your cash? (Finlay and Zorn, February 2023) — Vanguard Research
- Beginners’ Guide to Asset Allocation, Diversification, and Rebalancing — U.S. Securities and Exchange Commission
Last reviewed 1 October 2026.
This is general information, not advice for your circumstances. Rules and limits change; check the official source for your country, and consult a licensed professional before making financial decisions.