In short
- Allocation is the split between asset classes — mainly stocks and bonds. It is the choice that sets both the expected return and the size of the falls you have to sit through.
- The two move together: on an assumption of 7% real for stocks and 2% for bonds, shifting from 100/0 to 60/40 lowers the expected return from 7% to 5%.
- That costs time. For someone saving 30% of take-home from zero, the same shift moves financial independence from about 23 years to about 27.
- Bonds are not bought for return. They are bought to make the bad years smaller, which matters most in the years around retirement.
What allocation actually decides
Asset allocation is how a portfolio is divided between asset classes — in practice, mostly the split between stocks and bonds, with cash and sometimes property or commodities alongside.
It gets the attention it does because of what it controls. Research going back to the 1980s has found that for a given portfolio, the allocation explains most of the variability of returns over time — far more than which individual funds were chosen within each class. That finding is frequently misquoted as allocation explaining most of the level of returns, which is a different and less supportable claim, but the underlying point holds: the split matters more than the selection.
Why this guide sits underneath the others: Every calculator on this site asks for an expected return, and every projection depends on it. That number is not a free choice — it is largely determined by the allocation. Choosing 60/40 and then assuming a 7% real return is assuming the return of a portfolio you do not hold.
What each asset class contributes
- Stocks are claims on company profits. Historically the highest long-run returns of the major asset classes, and the highest volatility — declines of 30–50% have occurred repeatedly, with recovery periods measured in years rather than months.
- Bonds are loans, paying a defined income and returning the principal at maturity. Lower expected return, and generally much smaller declines. Their value falls when interest rates rise, which is why bonds are not risk-free and had a poor stretch when rates rose sharply.
- Cash does not fall in nominal terms and reliably loses purchasing power to inflation. It exists in a portfolio for spending needs and buffers, not for return.
The important point about bonds is that they are not held in the hope of outperforming. They are held because they usually fall less, and sometimes rise, when stocks fall — which means a mixed portfolio has smaller drawdowns and something that can be sold at a decent price when stocks are down.
What the trade costs
The expected return of a blend is the weighted average of its parts. Taking 7% real for stocks and 2% real for bonds — assumptions, not forecasts, and deliberately round — the arithmetic looks like this:
| Stocks / bonds | Expected return | Saving 30% | Saving 50% |
|---|---|---|---|
| 100 / 0 | 7.0% | 23 years | 15 years |
| 80 / 20 | 6.0% | 25 years | 15 years |
| 60 / 40 | 5.0% | 27 years | 16 years |
| 40 / 60 | 4.0% | 30 years | 17 years |
| 20 / 80 | 3.0% | 34 years | 19 years |
| 0 / 100 | 2.0% | 39 years | 20 years |
Two things are worth reading out of that table. The first is that the cost of holding bonds is real and measurable — four extra years for a 30% saver moving from 100/0 to 60/40. The second is that it is much smaller for a high saver: at a 50% savings rate the same shift costs one year, because contributions rather than returns are doing most of the work.
What the table cannot show: It gives every allocation a smooth constant return, which is exactly the thing bonds are held to change. The 100/0 row does not show the 40% drawdown that produced its higher average, or what selling into that drawdown would do to someone drawing an income. Expected return is only one half of the decision and the easier half to put in a table.
The age-based rules of thumb
The oldest shortcut is to hold your age in bonds — equivalently, 100 minus your age in stocks. Rising life expectancy produced more aggressive variants:
| Age | 100 − age | 110 − age | 120 − age |
|---|---|---|---|
| 25 | 75% | 85% | 95% |
| 35 | 65% | 75% | 85% |
| 45 | 55% | 65% | 75% |
| 55 | 45% | 55% | 65% |
| 65 | 35% | 45% | 55% |
These are shortcuts rather than findings, and the assumption underneath them is worth naming: that age is a good proxy for time horizon and for capacity to take risk. For someone retiring at the normal age that is roughly true. For a 35-year-old planning to stop at 45, and for a 70-year-old with a portfolio far larger than they will ever spend, it is not.
- Time horizon — how long until the money is needed, which for an early retiree is short even at a young age.
- Capacity to take risk — whether a large fall would actually change your plans, which depends on job security, other income, and how much margin the portfolio has.
- Willingness to take risk — whether you would hold through a 40% decline, which is a question about behaviour, and selling at the bottom converts a temporary fall into a permanent loss.
- What else you hold — a secure salary or an index-linked pension behaves somewhat like a bond holding, which is a common argument for holding fewer of them elsewhere.
Rebalancing
An allocation drifts. A 60/40 portfolio in which stocks outperform for several years quietly becomes 70/30 and then 75/25, carrying more risk than was chosen. Rebalancing means selling what has grown and buying what has lagged to restore the target.
- Calendar rebalancing — checking on a fixed schedule, commonly annually.
- Threshold rebalancing — acting only when a class drifts more than a set amount, often five percentage points, from its target.
- Rebalancing with contributions — directing new money to whatever is below target, which avoids selling entirely and is why it is simpler during accumulation than in drawdown.
Rebalancing is a risk-control measure rather than a return-enhancing one. It is also the point where costs and taxes enter: in a taxable account, selling to rebalance can realise a gain, which is why the contribution-based approach is often preferred where it is available.
Allocation around retirement
The conventional pattern reduces stocks steadily with age. Research on sequence of returns risk has produced an argument for something closer to the opposite in the specific window around retirement — a rising equity glidepath, holding more bonds at the point of retirement and increasing stock exposure over the following years.
The reasoning is that the risk is concentrated: the portfolio is at its largest and has just started to be drawn down, so a decline there does the most damage. Holding more bonds through that window and less afterwards targets the risk where it actually sits, rather than reducing risk uniformly with age.
This remains a debated approach rather than a settled one, and it interacts with the withdrawal strategy — flexible spending rules address the same risk by a different route. Which combination fits a particular retirement is not a question a general guide can answer.
Frequently Asked Questions
What is asset allocation?
It is how a portfolio is divided between asset classes, principally stocks and bonds. It sets both the expected return and the size of the declines the portfolio experiences, which is why it is generally treated as the most consequential portfolio decision — more so than which individual funds are chosen within each class.
What is a good stock and bond split?
There is no single answer, because the split trades expected return against the size of the falls you have to sit through. On an assumption of 7% real for stocks and 2% for bonds, moving from 100/0 to 60/40 lowers expected return from 7% to 5% — costing a 30% saver roughly four years to financial independence, but materially reducing drawdowns. The right balance depends on time horizon, capacity to absorb a loss, and whether you would hold through one.
Does the 100-minus-age rule work?
It is a shortcut rather than a research finding, and it assumes age is a good proxy for both time horizon and capacity to take risk. That assumption holds reasonably for a conventional retirement age and breaks down for early retirees, whose horizon is short while they are still young, and for people whose portfolio far exceeds what they will spend.
Should FIRE investors hold bonds?
The argument against is the return given up over a long accumulation phase; the argument for is that early retirement extends the drawdown period and therefore the exposure to a bad sequence of returns early on. The two arguments apply at different stages, which is why allocation is often described as something that changes across the plan rather than a single fixed choice.
How often should a portfolio be rebalanced?
Common approaches are annually, or whenever an asset class drifts more than about five percentage points from its target. During accumulation, directing new contributions towards whatever is below target restores the balance without selling anything, which avoids both transaction costs and, in a taxable account, realising a gain.
What is a rising equity glidepath?
Holding a higher bond allocation at the point of retirement and increasing stock exposure over the following years — the reverse of the conventional pattern. It targets sequence of returns risk, which concentrates in the window either side of the first withdrawal. It is a debated approach rather than an established one.
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The information and calculations provided are for informational and educational purposes only and should not be considered financial, investment, or professional advice. Projections are hypothetical, based on assumptions that may not reflect actual market conditions. Past performance does not guarantee future results, and all investments carry risk of loss. Consult a qualified financial professional before making financial decisions.