100 Minus Age Is Outdated: What the Four Allocation Rules Actually Assume

"Bonds should equal your age" is one of the most repeated rules in personal finance, and it produces a genuinely different answer than the glide path any real target-date fund actually follows. Neither is wrong, exactly — they're answering slightly different questions with different assumptions baked in. The problem is treating either one as a fact rather than a formula with a specific set of inputs.

The Minus-Age Family: One Formula, Three Popular Constants

"100 minus age" is really a family of rules that all share the same shape:

stockPct = clamp(X − age, 0, 100)
bondPct  = 100 − stockPct

The only thing that changes between versions is the constant X — commonly 100, 110, or 120. At age 35, that produces 65% stocks under the 100-rule, 75% under 110, and 85% under 120. All three are widely repeated rules of thumb with no single authoritative source — no regulator or academic study prescribes any of them. Higher X simply means more aggressive: it keeps more equity exposure through the working years and de-risks more slowly. The asset allocation by age calculator runs all three side by side against your actual age so the spread between them is visible rather than assumed.

"100 Minus Age" Is Literally "Bonds = Your Age"

These are the same formula stated two different ways. If bonds equal your age — 35% bonds at age 35 — then stocks are 100 minus that, or 65%, which is exactly what the 100-minus-age rule computes. Recognizing the equivalence matters because the two phrasings show up in different articles as if they were competing ideas, when they're identical arithmetic.

What Vanguard's Actual Glide Path Assumes Instead

Real target-date funds don't use a straight-line minus-age formula. Vanguard's published glide path moves through three distinct phases relative to a target retirement age R:

• A long hold zone. Equity stays flat at 90% from early accumulation until 25 years before retirement (age ≤ R−25).
• A pre-retirement glide. Equity declines linearly from 90% to 50% over the 25 years leading up to retirement (R−25 to R).
• A post-retirement glide, then a floor. Equity continues declining linearly from 50% to 30% over the seven years after retirement (R to R+7), then holds flat at 30% for the remainder.

For a standard R = 65 retirement age, that produces 90% equity at age 40, roughly 58% at age 60, exactly 50% at retirement, and 30% by age 72 onward — reproducing every anchor point Vanguard has published for its target-date strategy. Vanguard holds higher equity longer than any of the minus-age rules early in a career, then de-risks faster than all three of them do in the decade around retirement.

Why the Rules Diverge So Sharply

Run a 35-year-old through all four at the standard R = 65 retirement age: 100-minus-age says 65% stocks, 110-minus-age says 75%, 120-minus-age says 85%, and the Vanguard path says 90% — the most aggressive of the four, because age 35 still sits inside its 90% hold zone (25+ years from retirement). Run the same four rules at age 60: 40%, 50%, 60%, and roughly 58% respectively. The minus-age rules move in a straight line from day one; Vanguard's path is deliberately flat, then steep, then flat again — a shape no single constant X can replicate at every age simultaneously.

Retirement Age Changes Everything for Early Retirees

The minus-age rules ignore your target retirement date entirely — they're pure functions of current age. Vanguard's path is not: every anchor is defined relative to R, so moving the retirement age shifts the whole path. Someone targeting retirement at 55 instead of 65 sees Vanguard's 90% hold zone end at 30 instead of 40, 50% equity land at 55 instead of 65, and the 30% floor begin at 62 instead of 72 — a meaningfully more aggressive path through the working years than the standard-retirement-age version implies. That sensitivity is exactly why the asset allocation by age calculator exposes retirement age as its own input rather than hardcoding 65 — it's the tool in this cluster built with the Coast FIRE and Barista FIRE early-retirement audience specifically in mind.

What None of These Rules Actually Know About You

Every rule here takes exactly one input: age (and, for Vanguard, a target retirement date). None of them know your risk tolerance, your other assets, how stable your income is, or what your actual goals are. A rule that says "85% stocks at 35" isn't claiming that's optimal for you specifically — it's a starting convention, useful for orientation, not a substitute for weighing your own circumstances. The honest way to use any of these four numbers is as a reference point to compare your actual comfort level against, not an instruction to follow.

Splitting the Stock Sleeve

All four rules here answer only the top-level stock/bond question — none of them touch how the stock portion should be split between US and international holdings. Once you know your target equity percentage, the three-fund portfolio builder takes that number and computes exact dollar amounts across a US, international, and bond fund, and the guide on home country bias walks through how much international exposure is defensible. And because none of these rules account for drift once you've set an allocation, the portfolio rebalancing calculator — and the guide on why rebalancing is about risk control, not returns — covers what happens after you pick a target.

This guide is informational only and is not financial, investment, or tax advice. The minus-age figures are common rules of thumb, not standards; the Vanguard path is a model of its published glide-path anchor points, not the exact holdings of any specific fund. Consult a qualified financial professional before making investment decisions.

Frequently asked questions

Which of the four rules should I actually use?

None of them is objectively correct — the right choice depends on your risk tolerance, time horizon, and financial situation, none of which any age-based formula can see. A higher constant (120) or the Vanguard path in its early hold-zone years keeps more equity exposure for longer, which some investors prefer given a long horizon; a lower constant (100) is more conservative. Use these as reference points, not verdicts. The guide on which end of the spread to lean toward walks through the concrete factors — time horizon, income stability, other guaranteed income, sequence-of-returns risk — that argue for one end over the other.

Why does the Vanguard line stay flat and then drop steeply, instead of declining smoothly like the minus-age rules?

Vanguard's glide path is built in distinct phases: a long hold at 90% equity while retirement is more than 25 years away, then a steady linear decline to 50% by retirement, then a further decline to 30% over the following seven years, then a flat floor. The logic is that a long accumulation horizon can tolerate short-term volatility, while the years immediately around retirement need a faster reduction in risk. The minus-age rules, by contrast, decline in a straight line from the very first year — there's no hold zone.

Does the retirement age I enter change the minus-age rules too?

No — only the Vanguard path uses it. The three minus-age rules are pure functions of current age; retirement age doesn't factor into their arithmetic at all. If you're using this tool to plan around an early retirement date, the Vanguard comparison is the one that will actually reflect that choice.

How do I decide the US vs. international split within my stock allocation?

That's a separate decision from the stock/bond split covered here. Once you have a target equity percentage from one of these four rules, the three-fund portfolio builder lets you set a US/international split within that equity sleeve and computes the exact dollar amounts for each fund.

This guide is for informational and educational purposes only. It is not financial, tax, or legal advice. Tax rules are complex, fact-specific, and subject to change. Consult a qualified tax or financial professional before making IRA contribution or conversion decisions.

Last reviewed: September 2026 · Against primary sources cited in the body.