Retirement Planning: Will Your Money Last?
A different question
Every other lesson about investing has been about one motion: building the pile. Save, contribute, compound, diversify — grow the number. Retirement asks the opposite, and harder, question. You stop adding. You start spending the pile down. And the thing that decides whether retirement works is not how big the number got — it’s whether it lasts as long as you do.
That sounds like the same problem run backwards, but it isn’t. Spending a portfolio is genuinely different from growing one, for a reason we’ll get to: when you’re selling investments to pay the bills, the order the market’s good and bad years arrive in suddenly matters, not just the average. A retiree and a 25-year-old can earn the exact same average return over 30 years and have wildly different outcomes. First, though, the famous rule that started it all.
The 4% rule, and the “number” it implies
In the 1990s a financial planner named William Bengen asked a simple question: across every 30-year window in U.S. market history — including retiring right before the 1929 crash, the 1970s stagflation, every bad start you can imagine — what’s the most you could have withdrawn each year without running out? His answer, refined by the well-known Trinity study, became the most quoted rule in retirement planning:
Withdraw about 4% of your portfolio in the first year. Raise that dollar amount with inflation each year after. A stock-and-bond portfolio survived 30 years in the vast majority of historical cases.
Notice the shape of it. You don’t withdraw 4% every year — you withdraw 4% the first year and then just give yourself an inflation raise, so your spending power stays flat while the percentage floats with the market. The point of the rule is to set that first-year number.
And it comes with a beautifully simple corollary. If a safe withdrawal is 4%, then the pile you need is just your annual spending divided by 4% — which is 25 times your spending (because 1 ÷ 0.04 = 25):
- Spend $40,000 a year? Your number is about $1,000,000.
- Spend $60,000? About $1,500,000.
- Want to be more conservative and draw 3%? Multiply by 33× instead.
This is what people mean by “your number.” It’s not a mystery you need a calculator to divine — it’s a multiple of how you actually live.
The master lever is the RATE, not the pile
Here’s the mental shift the simulator is built to drill in. A million dollars is not “enough” or “not enough” on its own — it depends entirely on what you spend. $1,000,000 supporting $40,000 of spending is a 4% withdrawal rate and very likely lasts. The same $1,000,000 supporting $80,000 is an 8% rate and very likely doesn’t. Same pile, opposite outcome.
So the number that governs everything is your withdrawal rate = annual spending ÷ nest egg. Drag the spending slider up and watch the “chance money lasts” fall off a cliff — not gently, a cliff — as the rate climbs past 4%, then 5%, then 6%. That cliff is the whole game. Retirement security is a question about a ratio, and the slider you control most easily is spending.
The shaded cone is the range of futures the same plan could produce — the band between a good (top-10%) and bad (bottom-10%) sequence of markets, with the typical path through the middle. When the plan is healthy the whole cone floats above the axis. When it isn’t, the lower edge dives to the $0 floor — that’s money running out. Push spending up and watch the bottom of the cone sink toward zero years earlier.
Sequence-of-returns risk: why order matters
Now the deep idea, the one that makes decumulation its own beast.
While you were saving, the order of returns didn’t really matter. A 50% crash early in your career is almost a gift — you’re buying cheap for decades afterward, and by retirement the average is all that shows up. But in retirement you’ve flipped from buyer to seller. Every year you sell some investments to fund your life. And selling into a crash is the opposite of buying into one: you have to liquidate more shares to raise the same dollars, locking in the loss and leaving fewer shares to recover when the market bounces back.
So a bad run in the first few years of retirement can permanently sink a portfolio — even if the market later delivers a perfectly normal long-run average. The same returns in a kinder order — good years first, the bad run arriving after the balance has grown a cushion — sail through. That’s sequence-of-returns risk, and it’s why the years right around your retirement date are the most dangerous ones of your financial life.
You can see it in the simulator without changing your average return at all: pick a more volatile market mix and the “chance money lasts” drops, even though the typical return is higher. More volatility means more chances to hit a bad early sequence. Average return decides whether you can make it; the order decides whether you do.
What actually protects you
Sequence risk sounds grim, but the defenses are concrete and mostly free:
- Keep the rate sane. 4% is the famous anchor for a 30-year retirement. If you retire early and need the money to last 40–50 years, drop to 3–3.5% — the longer the horizon, the lower the safe rate, because there are more chances to meet a bad sequence.
- Hold a cash buffer. A year or two of spending in cash or short bonds means that when the market craters, you can spend that instead of selling stocks at the bottom. You’re letting the portfolio recover instead of liquidating it into the hole. This is the single most effective antidote to sequence risk.
- Stay flexible. The 4% rule assumes you spend the same inflation-adjusted amount no matter what. Real retirees don’t — they trim a little in bad years (skip the big trip, defer the new car). Even small, temporary cuts during a downturn dramatically raise the odds the money lasts. Flexibility is the cheapest insurance in personal finance.
- Don’t over-bond, either. Going too conservative has its own failure mode: a portfolio that can’t out-grow inflation over 30 years bleeds out slowly instead of dramatically. You need enough growth to outrun rising prices. Notice in the sim that the safest-looking mix isn’t always the one most likely to last.
FIRE is the same math, stretched
FIRE — Financial Independence, Retire Early — is just this lesson with the dials turned up. “Financial independence” means your number is covered: your portfolio at a safe withdrawal rate funds your life, so paid work becomes optional. The arithmetic is identical — your number is still a multiple of your spending — but two things change. Your horizon might be 50 years instead of 30, which argues for a lower safe rate (more like 3.25–3.5%). And the lever FIRE leans on hardest is spending, because a lower annual spend shrinks your number twice over: you need less income and a smaller multiple of it. Cutting spending from $60k to $40k doesn’t just save $20k a year — it drops your number from $1.5M to $1.0M.
The durable lessons
- Think in withdrawal rates, not dollar piles. “Is $1M enough?” has no answer until you say what you’ll spend. Spending ÷ pile is the number that decides everything.
- Your number is ~25× your spending at a 4% rate (33× at 3%). It’s a multiple of your life, not a mystery.
- The order of returns matters, not just the average. A bad early run is the real danger of retirement, because you’re selling into it. That’s sequence-of-returns risk.
- The defenses are cheap and boring: a sane rate, a cash buffer so you never sell at the bottom, and the flexibility to trim spending in a bad year. The 4% rule is a sturdy starting point — a rule of thumb that has held up remarkably well — not a guarantee you can set and forget.