How Long Should You Plan to Live? The 85th-Percentile Rule
Life expectancy is an average. Half of everyone that age outlives it. The real question a retirement plan needs answered isn't "what's typical" — it's "what's the age I have a real chance of living past."
- Life expectancy is the mean of a distribution, not a safe planning number — roughly half of people at any given age go on to live longer than it.
- A more honest target is a survival percentile: the age you have, say, only a 15% chance of living past — computed directly from the SSA's own actuarial mortality table, the same one underneath the app's own planning tools.
- Married couples need to plan even longer than either spouse's individual number. The plan has to survive until the second death, not the first, and that "last survivor" age is always later than either person's own horizon.
Why life expectancy is the wrong number to plan to
Ask most people how long to plan for and they reach for one number: life expectancy. For a 60-year-old, that's roughly the low-to-mid 80s. It feels concrete, it comes from a real government source, and it slots neatly into a spreadsheet. It's also, for planning purposes, close to the worst single number available — not because it's wrong, but because of what "average" actually means.
Life expectancy is the mean of a distribution of ages at death, and a mean has a defining property: roughly half of the population it describes ends up on either side of it. For a 60-year-old, that means something close to a coin flip on whether they'll still be alive past their own life expectancy. A retirement plan built to run out of money exactly at the average age of death has, by construction, something close to a 50% chance of running out while its owner is still alive.
The average isn't a floor. Half the distribution lives past it — and running out of money on the way there is the actual risk this whole decision is about.
That asymmetry is the entire case for planning past the average instead of to it. Retiring with a plan that lasts three extra years you didn't strictly need is a minor inefficiency — a bit more caution than turned out to be necessary. Retiring with a plan that runs dry three years before the actual end of a real life is a crisis, and it lands at the worst possible time to fix it. The two failure modes aren't symmetric, so the planning number shouldn't be picked as if they were.
The real math: a survival curve, not a guess
The honest alternative isn't a bigger guess — it's a different question. Instead of "what's the average age of death for someone like me," ask "what age do I have a real, non-trivial chance of living past." That's a survival percentile, and it comes straight out of the same SSA Period Life Table (2022) that powers the app's own Planning Horizon Workshop.
The table tracks, for every age and sex, how many people out of an original 100,000 births are still alive at that age (the "lives" column). Survival probability from a current age to any future age is just a ratio of two numbers from that column: S(age) = lives at that age ÷ lives at your current age. Run that ratio out year by year and it traces a curve — 100% survival at your current age, declining smoothly toward zero somewhere past 100. A planning horizon at a chosen percentile is simply the oldest age where that curve is still at or above the corresponding survival level. The tool below runs that exact calculation, live, off the real table — nothing simulated, nothing estimated.
Source: SSA Office of the Chief Actuary, Period Life Table, 2022 — the same table embedded in the app's own Planning Horizon Workshop. "Blended" averages the male and female columns; toggle to your own sex for a more specific curve. A period table freezes 2022 mortality and doesn't account for future medical improvement, and this is a population-wide average — both of those biases mean the real number for a healthy, insured household likely runs a bit longer than shown here, not shorter.
A worked example
Take a 60-year-old, blended sex, with no other information. Running the survival curve above at three different percentiles gives three very different "how long should I plan for" answers from the exact same starting point:
| Target | Planning horizon | Read |
|---|---|---|
| Mean life expectancy | Age 83 | The "coin flip" number — close to a 50/50 chance of living past it |
| 50th percentile | Age 83 | Same as the mean here — median and mean land close together |
| 85th percentile | Age 92 | Only ~15% of 60-year-olds are still alive at this age — a real hedge against a long life |
| 95th percentile | Age 97 | A conservative, near-worst-case planning horizon |
The gap between the mean and the 85th percentile — nine full years, in this example — is nine years of retirement income a plan built to the average simply never accounted for. That's not a rounding error. It's the entire difference between a plan that's honestly hedged against a long life and one that's quietly betting on an average outcome.
Why couples need to plan even longer
Everything above describes one person. A married household is a different, harder question, because the plan doesn't stop needing income when the first spouse dies — it has to keep going until the second one does. That "last survivor" horizon is mathematically always later than either spouse's own individual planning age, because the household only fully exits the picture once both people are gone, and "at least one of two people is still alive" is always a higher-probability event than "this one specific person is still alive."
Run two 60-year-olds, both blended sex, through the same 85th-percentile question, and the individual horizon of 92 becomes a household horizon of roughly 95 — three years later than either spouse's own number, purely from the arithmetic of two independent chances instead of one. For a household planning around a joint pension, a shared portfolio, or a surviving spouse's Social Security, that gap is the difference between a plan that quietly assumes someone dies on schedule and one that's actually built for how households really end.
What this doesn't capture
This tool is deliberately simple, and it's worth being direct about the limits. It uses a period life table, meaning it freezes 2022 mortality rates rather than projecting future medical improvement — historically, life expectancy has trended upward over time, so this likely understates how long someone retiring today will actually live. It's also a population-wide average across everyone at a given age, and people with the means and inclination to seriously plan a retirement tend to be more affluent, more insured, and healthier than that population on average — another reason the real number likely runs a bit higher, not lower. And it only knows age and sex — it has no way to factor in your own health, smoking history, or family longevity, all of which move the real answer meaningfully in either direction for any individual. Every one of these gaps points toward the same conclusion: treat the horizon this tool shows as a floor worth respecting, not a ceiling.
How this is calculated
Survival probability to any future age is the ratio of two numbers in the SSA table's "lives" column: how many of an original 100,000 births are still alive at the target age, divided by how many are still alive at your current age. A planning horizon at percentile p is the oldest age where that survival probability is still at or above (1 − p) — for the 85th percentile, the oldest age with at least a 15% survival probability remaining. For couples, joint survival is 1 − (1 − your survival) × (1 − your spouse's survival) at each point on a shared calendar timeline, which is why it's always higher than either person's own number alone. This is the identical math behind the app's Planning Horizon Workshop — deterministic table lookups, not a simulation, and nothing you enter here is sent anywhere. The complete methodology, including the table's source and refresh schedule, is documented in the trust framework.
Common questions
This tool sets a suggested planning horizon. The full app uses it to run your actual withdrawal plan against thousands of market scenarios — and models the survivor transition for couples automatically.
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