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Lump sum or dollar-cost average?
Enter the windfall, your assumed return, the horizon, and the DCA period.
X VS Y COMPARISON · MONEY
Lump Sum vs Dollar-Cost Averaging
Got a windfall — inheritance, bonus, sale proceeds — and wondering whether to invest it all at once or drip it in monthly? Run the math: month-by-month simulation, the dollar gap between the two, and the historical reason one usually wins.
How this comparison works
The calculator runs both strategies on the same monthly timeline. Lump sum invests the whole windfall on day one, so every dollar compounds for the full horizon. Dollar-cost averaging splits the windfall into equal monthly investments; dollars invested later compound for fewer months, and the uninvested cash earns nothing in this model. Both use the same assumed return, so the only difference is timing.
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Lump-sum end value | W × (1 + i)n | What the windfall grows to if invested on day one. i = monthly return, n = months. |
| DCA end value | Σ pmt × (1 + i)n−k | Each monthly slice compounds only for its remaining months, so later slices contribute less. |
| Lump-sum edge | lump FV − DCA FV | The dollar cost of waiting: $3,708 on the $50k / 7% / 10-yr / 12-mo defaults (3.8%). |
| DCA monthly investment | W ÷ m | How much goes in each month while averaging in: $4,166.67 on the defaults. |
Why lump sum usually wins
Markets rise more often than they fall. Research by Vanguard across 1,000+ historical 12-month windows in the US, UK, and Australia found that lump-sum investing beat dollar-cost averaging roughly two-thirds of the time — not because anyone can time the market, but because early dollars get more time in a market that trends up. DCA isn’t a return strategy; it’s regret insurance: it feels much better if the market drops right after you start.
Who uses this
- Windfall recipients: inheritance, house sale, or IPO proceeds — put numbers on the wait-vs-invest decision.
- Bonus season planners: annual bonus just landed — see what dripping it in over 6 or 12 months actually costs.
- Advisors & planners: a clean illustration for the “invest it now” conversation with nervous clients.
- Students & researchers: a worked, citable comparison of two canonical investing strategies — cite it below.
Accuracy & limitations
This model uses one constant return and monthly compounding — real markets are lumpy, and a crash right after you lump-sum in is the scenario DCA protects against. Taxes, fees, and inflation are not modeled (use a real return to approximate inflation), and uninvested DCA cash is assumed to earn 0%. Treat the gap as illustrative of the timing effect, not a prediction of your portfolio.
Investing the windfall at all is the main event — the method is the garnish. For the full reasoning, see the guide Lump sum or dollar-cost average: which wins?, and model steady monthly investing from income with the compound growth calculator.
Cite this calculatorBright Side Kit. “Lump Sum vs Dollar-Cost Averaging.” brightoolbox.com, 2026.
Bright Side Kit. "Lump Sum vs Dollar-Cost Averaging." https://brightoolbox.com/lump-sum-vs-dollar-cost-averaging/ Accessed October 22, 2026.Frequently asked questions
Is lump sum investing always better than dollar-cost averaging?
No — but the math favors it roughly two-thirds of the time, because markets rise more often than they fall and early dollars compound longer. DCA wins when markets drop early in the period. The catch: you only know which one won in hindsight.
What did the Vanguard study on lump sum vs DCA actually find?
Vanguard’s widely cited research compared both strategies across more than 1,000 historical 12-month windows in the US, UK, and Australia. Lump-sum investing produced a higher ending value about 68% of the time — a consistent result across all three markets.
What if the market crashes right after I invest a lump sum?
That’s the exact scenario dollar-cost averaging insures against — and the main honest argument for it. DCA buys emotional protection: a crash hurts less when only part of your money is in. If a 20% drop next month would make you sell everything, DCA (or a more conservative mix) beats a lump sum you’d abandon.
Does dollar-cost averaging guarantee better returns?
No — that’s the most common misconception. DCA reduces timing regret, not expected return. On average it costs a few percent of the windfall (3.8% in our $50k default example) in exchange for a smoother emotional ride.
What return should I assume in the calculator?
For a stock-heavy portfolio, 6–8% nominal (before inflation) is the usual long-run assumption; use 4–5% for a balanced mix. Run it twice — once at your best guess, once two points lower — and notice the ranking of the two strategies barely changes.
Do taxes change the answer?
The account matters more than the method. Filling tax-advantaged space first (401(k), IRA, HSA) usually beats either timing choice. Within the same account, lump sum and DCA face identical tax treatment on the dollars that are invested.
Should I stretch DCA over more than a year?
Longer DCA periods make the underperformance worse on average — more dollars sit in cash longer while the market trends up. Most research tests 6–12 months; beyond a year you’re mostly paying for comfort. If you need two years to feel safe, consider whether the asset mix is too aggressive.