What a withdrawal projection is really doing
Underneath the friendly output, the model runs a month-by-month simulation. It starts with your balance, applies one month of growth, subtracts your scheduled withdrawal, and repeats. Every month the surviving balance earns a little more, and every month you take a little out. The projection just keeps score until the balance either runs to zero or clearly outlasts a very long horizon.
The Retirement Withdrawal Calculator applies the annual return divided across twelve months, so a 5% yearly return becomes roughly 0.417% a month on whatever balance remains. Withdrawals land on the schedule you pick — monthly, quarterly, or yearly — and can be taken at the start or end of each period. That timing choice is small but real: taking money out before it grows leaves slightly less to compound.
Because the math compounds, the result is sensitive to its inputs in a way that is easy to underestimate. Two plans that look almost identical on paper can end up decades apart, which is exactly why leaning on the single headline figure is risky.
A worked example with the calculator's defaults
Take the calculator's default scenario: a starting balance of $600,000, a fixed withdrawal of $3,000 a month, a 5% expected annual return, 3% inflation, and withdrawals taken at the end of each month with no fees or tax applied.
First, the withdrawal rate. You draw $3,000 twelve times, which is $36,000 in year one. Divide that by the $600,000 balance and you get a 6.0% withdrawal rate — noticeably higher than the 4% figure people often quote as a rule of thumb.
Now follow year one. The remaining balance earns about $29,861 in growth across the twelve months, while $36,000 leaves the account. Net, the balance slips from $600,000 to roughly $593,861. It barely moves, which can lull you into thinking the plan is comfortable. Run the same mechanics forward and the balance is projected to hit zero at about month 431 — roughly 35.9 years. On a 5% return, the money lasts almost 36 years.
Worked example
Why the headline number is fragile
Almost 36 years sounds reassuring. But that figure rests entirely on the 5% return holding steady, and returns are the least reliable input in the whole exercise. Change nothing else and drop the assumed return to 2% — a plausible stretch for a cautious portfolio or a rough decade — and the same $600,000 with the same $3,000 draw is projected to last only about 20.3 years. One assumption moved by three percentage points, and the plan lost roughly fifteen years.
That is the core lesson: the output is not a measurement, it is a consequence of your guesses. The calculator even reports the break-even return — the growth rate at which the balance would essentially never run down. For this scenario it is about 5.98%, just above the 6% withdrawal rate. You are relying on returns to almost exactly match what you are pulling out, which leaves very little cushion.
This is why the tool labels the default plan as aggressive rather than comfortable. It is not judging you; it is flagging that the margin is thin.
Inflation quietly shrinks the paycheck
A fixed $3,000 monthly withdrawal looks stable, but its buying power is not. At 3% inflation, that $3,000 buys what about $2,232 buys today after ten years, and around $1,661 after twenty. The number on the statement never changes; what it can purchase keeps falling.
The calculator captures this by comparing your nominal return against a real return — return after inflation. Here the real return works out to roughly 1.94%, well below the 6% withdrawal rate. So even in the years the balance appears to hold up in dollar terms, its purchasing power is eroding underneath. A plan can look like it is surviving while quietly failing to keep you at the same standard of living.
If holding your lifestyle steady matters, an inflation-adjusted withdrawal style keeps the buying power constant but drains the portfolio faster — another trade-off the tool lets you test directly.
Stress-test with three levers, not one answer
The honest way to use any withdrawal estimate is to run it several times and read the spread. Three levers do most of the work: the return, inflation, and the withdrawal amount. Nudge each one toward a worse case and see how far the outcome moves.
A useful habit is to build a base case, a lower-return case, and a higher-inflation case, then look at the gap between them. If your plan only survives when returns are strong and inflation is tame, that is worth knowing before you retire, not after. The calculator's scenario view does this side by side, and its sequence-of-returns view goes further by testing what happens if the bad years arrive early rather than late — a risk a single average return can hide entirely.
The 401(k) Calculator and a broader retirement projection help on the accumulation side, but the withdrawal question deserves the same range-based caution. You can review how these estimates are built on our methodology page.
A simplified example: sequence risk while withdrawing
Sequence risk bites harder during withdrawals than during accumulation, because you're pulling a fixed dollar amount out of a shrinking-or-growing base at the same time markets move. A simplified two-year illustration (not the calculator's monthly engine, but the same idea) makes this concrete: two retirees each start with $600,000, each withdraw $36,000 at the end of every year, and each experiences the identical two annual returns — just in a different order.
Retiree A gets the bad year first: a −20% return in year one, then +40% in year two. Year one: $600,000 × 0.80 = $480,000, then withdraw $36,000 → $444,000. Year two: $444,000 × 1.40 = $621,600, then withdraw $36,000 → $585,600.
Retiree B gets the same two returns in reverse: +40% first, then −20%. Year one: $600,000 × 1.40 = $840,000, then withdraw $36,000 → $804,000. Year two: $804,000 × 0.80 = $643,200, then withdraw $36,000 → $607,200.
Same two returns, same withdrawals, same starting balance — yet Retiree B ends the two years with $607,200 versus Retiree A's $585,600, a gap of $21,600. The bad year hurts more when it comes first, because the fixed withdrawal comes out of a smaller balance after the crash, permanently reducing the capital left to benefit from the recovery that follows. This is exactly why the calculator's average-return projection and its sequence-of-returns view can tell two very different stories from the same average number.
The withdrawal rate that actually matters
The 4% figure referenced below comes from historical U.S. market research (the "Trinity study" and similar work) testing what starting withdrawal rate a portfolio could sustain over a 30-year retirement across many historical market sequences, with the withdrawal amount then adjusted for inflation each year. It's a starting point for conversation, not a law of nature — the original research used specific historical data, specific asset allocations, and a specific 30-year horizon, none of which necessarily match your situation.
A fixed-dollar withdrawal (like the $3,000/month default here) and an inflation-adjusted withdrawal behave differently under stress: fixed-dollar withdrawals take a shrinking real bite out of a falling portfolio, since the dollar amount doesn't grow even as inflation erodes its value, while inflation-adjusted withdrawals protect purchasing power but can drain a struggling portfolio faster. Some retirees use a dynamic approach instead — cutting withdrawals in years the portfolio falls and only fully restoring them once it recovers — trading a variable income for a longer-lasting portfolio.
Common mistakes
- Trusting the single 'your money lasts X years' figure as if it were a forecast — it is only as good as the return you assumed, and returns are the most uncertain input.
- Confusing the withdrawal rate with the 4% rule of thumb: $3,000 a month on $600,000 is a 6% rate, not 4%, which changes the risk picture entirely.
- Ignoring inflation on a fixed withdrawal — a steady $3,000 loses roughly a quarter of its buying power in ten years at 3% inflation.
- Assuming a smooth average return, which hides sequence-of-returns risk: a poor first few years does far more damage than the same losses later on.
- Leaving fees and tax at zero. Real accounts carry expense ratios and withdrawals are often taxable, both of which shorten how long the money lasts.
- Setting the return equal to or just above the withdrawal rate and treating that as safe — it leaves almost no cushion for a weak decade.
- Treating a 4% (or any) withdrawal-rate rule of thumb as personally guaranteed. It's a historical reference point from specific past data, not a promise about your specific portfolio, time horizon, or tax situation.