The Glide Path
A glide path is the schedule by which a portfolio's equity weight declines as a target date approaches. Its purpose is to reduce exposure during the years when a large fall would be hardest to recover from, and the specific shape of it is a judgment rather than a calculation.
A glide path is an answer to a specific question: when does a large fall stop being survivable. It is not a general statement that risk should decline with age, and treating it as one produces portfolios that are conservative for decades longer than they need to be.
How it works
The equity weight starts high and declines toward a target date. The bond weight rises to match, and the transition happens gradually rather than at any single moment.
Early on, a fall is survivable because time is available. A 40% decline twenty-five years from the date is unpleasant and not consequential — the recovery arithmetic has decades to work in.
Near the date it is a different event entirely. The balance is at its largest, withdrawals are about to begin, and there is no time to wait — which is the whole reason the path exists.
The vulnerable window
Sequence risk is concentrated, not spread evenly across a lifetime. The years immediately before and after the date combine the largest balance with the start of withdrawals, and a poor sequence there does damage a good decade afterwards cannot undo.
In the S&P 500 since 1950, 93% of trading days closed below the previous record, the deepest fall was 56.8%, from 2007 to 2009, and the longest wait for a new record was 7.5 years, from 1973 to 1980 — and the index still went on to new records. Being below a high is normal; needing to sell while below one is the actual problem. Measured on S&P 500 daily closes from 1950 through September 2026, excluding dividends.
Which means the glide path is buying insurance for a specific window rather than being generally cautious.
A worked example
Take a $1,000,000 portfolio in a market that falls 40%, two years before the date.
At 90% equities it falls to 640,000 and needs a 56.25% gain to recover.
At 55% equities it falls to 780,000 and needs 28.21%.
At 30% equities it falls to 880,000 and needs 13.64%.
All three then have to support withdrawals from wherever they landed. The gap between the first and third is 240,000 of capital at the exact moment the plan starts drawing on it.
The rules of thumb
“Age in bonds” says hold your age as a percentage in bonds — 40% at forty, 65% at sixty-five. It is memorable and it is not derived from anything.
Most commercial glide paths are considerably more aggressive, often holding well over half in equities at the target date, on the reasoning that a retirement lasting thirty years still needs growth.
Both are defensible and neither is a calculation. The honest position is that the shape is a judgment about a trade-off, and it should be a knowing one.
To or through
A path that glides to the date reaches its most conservative allocation there and holds it. A path that glides through keeps reducing equities for ten or twenty years afterwards.
The second implies a much longer decumulation and a lower final equity weight, and the two produce materially different portfolios from the same target year.
Some designs deliberately rise again after the date, on the argument that the vulnerable window ends once the first years of withdrawals have passed. That is a serious proposal rather than a contradiction, and it follows directly from where sequence risk actually sits.
Costs
Gliding means trading, continuously and forever. Every purchase and sale pays the spread between bid and ask, and inside a fund those costs are borne by every holder.
A gradual path trades small amounts often; a stepped one trades large amounts rarely. The gradual version is generally cheaper in a fund and more awkward to run by hand.
The original data
Among the 24,971 unique videos in the search study behind this site, the nearest subject is workplace plans, in 22 videos at a median of 81,626 views.
The glide path is the schedule that determines how much equity risk a target-date fund carries into retirement, and it is set by the fund provider rather than by you.
The question: Five years out and equities are running. Delay the glide?
The answer is that the glide exists precisely for the case where the run does not continue. Delaying it is a forecast, taken at the point where the balance is largest and a fall would do the most damage. The insurance is being canceled exactly when the premium looks most wasteful, which is the pattern for every kind of insurance.
When it fails
A glide path calibrated to a date can be wrong about the date, and that error compounds in both directions. Someone who retires five years early meets the vulnerable window with an allocation still built for someone working, and someone who works five years longer spends those years far more conservatively positioned than their actual horizon warranted. The schedule was correct for the plan it was given, and the plan changed — which is the ordinary case rather than the exception.
The second failure is treating age as the input. The horizon and the capacity are the inputs; age is a proxy for them.
A third is assuming to and through are interchangeable. They produce different portfolios.
A fourth is running one alongside other holdings. The overall allocation is then nobody’s design.
A fifth is delaying the glide after a strong run. That is a market call.
And a sixth is treating the endpoint as safe. A conservative portfolio still has to outpace inflation for thirty years.
Related
Target-date funds are the product this schedule sits inside. Withdrawal strategy is the problem it was preparing for. And time horizon is the input it is really a proxy for.
What makes this worth understanding rather than delegating is that the vulnerable window is narrow and specific: a few years either side of the date, when the balance is largest and the first withdrawals begin. Everything before that window can afford to be aggressive and everything after it is a different problem again.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.