If you’re investing a windfall for the long term, putting it in all at once has historically beaten spreading it out about two-thirds of the time. That’s the finding of Vanguard’s 2023 study. Dollar-cost averaging (DCA) over a few months is still a reasonable choice if a sudden drop right after investing would make you panic and sell, because DCA beats leaving the money in cash. A common middle path is to invest half now and the rest over three to six months.
Here’s what the research says, how to decide, and a step-by-step plan for an inheritance, bonus, stock sale or home sale that could move your FIRE date.
Lump sum vs. dollar-cost averaging: what the research says #
In February 2023, Vanguard published Cost averaging: Invest now or temporarily hold your cash? It compared investing a lump sum immediately against spreading the same money over time, across several markets, historical periods and simulations. The key results:
- Lump sum beat cost averaging about 68% of the time in the historical data.
- Cost averaging still beat holding cash about 69% of the time.
- From 1976 to 2022, U.S. stocks beat 3-month Treasury bills in 76% of the periods studied, which is why waiting usually costs you.
The logic is simple. Markets rise more often than they fall, so money waiting on the sidelines usually misses gains. The more stock in the portfolio, the bigger lump sum’s average edge.
What the averages hide is the other third of the time. If you invest $200,000 on Monday and stocks fall 20% over the next few months, you’ll feel it. The cost that matters isn’t the math, it’s what you do next. Someone who sells in fear after a lump-sum drop does far worse than someone who dollar-cost averaged and stayed invested.
How to decide #
| If this describes you | Consider |
|---|---|
| You’ve held through a big market drop before without selling | Lump sum |
| The windfall is small compared with your existing portfolio | Lump sum |
| The windfall is most of your net worth and you’re new to investing | DCA over 3 to 12 months |
| You’re torn | Half now, the rest in equal monthly amounts over 3 to 6 months |
Whatever you choose, write down the schedule in advance and automate it. DCA only works if you actually keep buying when prices fall.
A step-by-step plan for investing a windfall #
Step 1: Park it and wait 30 to 90 days #
Put the money somewhere safe and boring, such as a high-yield savings account, a money market fund or Treasury bills, and make no big decisions for a month or two. The goal is to avoid impulse purchases, pushy sales pitches and decisions made while excited or grieving.
Step 2: Understand the tax situation #
Different windfalls come with different tax rules:
- Inherited taxable investments usually get a step-up in cost basis to their value at the date of death, so selling soon after inheriting often creates little or no gain.
- Inherited traditional IRAs and 401(k)s are taxed as income when withdrawn. Most non-spouse beneficiaries must empty the account within 10 years, and some must also take yearly withdrawals during that time. Spreading withdrawals across low-income years can save a lot of tax.
- Bonuses are ordinary income, and withholding often doesn’t cover the full tax.
- Company stock or a business sale may have large gains. The timing of a sale across tax years can matter.
For anything large or complicated, a one-time session with a fee-only planner or CPA is money well spent.
Step 3: Pay off high-interest debt #
A credit card at 20% or more is a guaranteed 20% return when you pay it off, and no investment reliably beats that. Personal loans and high-rate car loans are next.
Low-rate debt is a judgment call. Paying off a mortgage is a guaranteed return equal to its rate and lowers the spending your FIRE number has to cover. Investing usually earns more over long periods, but not every year. We look at the savings-rate side in does paying off your mortgage count toward your savings rate.
Step 4: Set aside money for near-term plans #
Money for anything in the next few years (an emergency fund, a home purchase, a car, a sabbatical) shouldn’t go into stocks. See investing for mid-term goals for how to hold it.
Step 5: Fill tax-advantaged accounts #
You can’t deposit a windfall straight into a 401(k), but you can get it there indirectly:
- 401(k), 403(b) or TSP: raise your payroll contribution toward the $24,500 limit for 2026 (plus $8,000 catch-up at 50 and older, or $11,250 at 60 to 63), and use the windfall to cover the smaller paychecks.
- IRA: contribute up to $7,500 for 2026 (plus $1,100 at 50 and older), for yourself and a spouse. Limits come from the IRS.
- HSA: up to $4,400 self-only or $8,750 family for 2026, if you’re on an eligible plan.
Step 6: Invest the rest in a taxable account #
Broad, low-cost index ETFs are the default for taxable money, since they rarely distribute capital gains. Put tax-inefficient holdings like bonds and REITs in your retirement accounts where you can. Minimizing dividend tax drag explains why.
Step 7: Spend a little on purpose #
Set aside 1% to 5% for something you’ll enjoy, guilt-free. It helps you stick to the plan for the rest.
Did the windfall change your FIRE type? #
A large windfall can move you from “still saving hard” to Coast FIRE, where existing savings will grow to your retirement target with no more contributions. If that’s you, you might downshift to a lower-stress job now rather than retiring early. Our guide on calculating your Coast FIRE number shows how to check.
This is where seeing the new numbers helps. In Retire Goals, you log the windfall as a contribution to the right goal and watch the projected finish date move, with the Monte Carlo odds updated alongside it. The Coast FIRE calculator tells you the amount that grows to your FIRE number by your chosen retirement age with no more saving. If your new balance is above that, you’ve crossed the line. No bank connection is needed, and everything stays on your phone.
Frequently asked questions #
Is it better to invest a lump sum or dollar-cost average? #
Historically, a lump sum has done better about two-thirds of the time, because markets rise more often than they fall. DCA reduces the chance of regret from investing just before a drop, and it still beats sitting in cash. Choose the one you’ll stick with through a downturn.
How long should I spread out a DCA plan? #
Three to twelve months is typical. Longer schedules leave more money in cash for longer, which usually costs returns. Set the dates in advance and automate them.
Should I pay off my mortgage with a windfall? #
It depends on the rate, your other savings and how much you value being debt-free. Paying it off earns a guaranteed return equal to the mortgage rate and lowers your spending in retirement. Investing has usually earned more over long periods, but with risk. Many people split the difference.
What should I do first with an inheritance? #
Park it safely, find out the tax rules for each account you’ve inherited (especially the 10-year rule for inherited IRAs), and pay off high-interest debt. Then invest according to a written plan. If the amount is large, a fee-only planner or CPA can help you avoid expensive mistakes.