Why the split matters more than the picks
Broad asset classes behave differently enough that the mix dominates the outcome. Stocks have historically delivered the highest long-run returns and the deepest drawdowns; high-quality bonds return less and fall less; cash returns least and does not fall in nominal terms but loses purchasing power to inflation.
Choosing 80% stocks versus 40% stocks changes your expected return and, more importantly, changes how much you can lose in a bad year. Choosing between two similar global index funds changes approximately nothing by comparison.
Start with time horizon
The single most useful input is when you need the money, because that determines whether you can wait out a fall.
| Money needed in… | Reasonable default | Why |
|---|---|---|
| Under 2 years | Cash / deposits | No time to recover from any fall |
| 2–5 years | Mostly bonds and cash | Equity drawdowns commonly last years |
| 5–10 years | Balanced mix | Some recovery time, but not unlimited |
| 10+ years | Mostly equities | Time to absorb multiple market cycles |
Notice that this is about the money's horizon, not your age. A 60-year-old's retirement pot may still have a 25-year horizon; a 25-year-old's house deposit has a three-year one. Most people hold several pots with different horizons, and each deserves its own allocation.
Then check capacity and willingness to take losses
Horizon sets the ceiling. Two other things set the floor:
- Capacity for loss — what happens materially if the money falls 40%. If it delays retirement by a decade or means a child cannot start university, capacity is low regardless of how brave you feel.
- Willingness — whether you would actually hold through it. An allocation you abandon at the bottom is worse than a more conservative one you keep. The failure mode is not volatility; it is selling into it.
The stress test worth doing
Take your intended allocation and assume equities fall 40% while bonds hold flat — roughly the scale of several real bear markets.
- 100% equities, $100,000 → falls to $60,000
- 80 / 20 → $100,000 becomes $68,000
- 60 / 40 → $100,000 becomes $76,000
- 40 / 60 → $100,000 becomes $84,000
Read those as real amounts of your own money, not percentages. The largest number you could see on a statement without selling is your allocation.
What the age rules get right and wrong
“Hold 100 minus your age in stocks” (or 110, or 120) is a mnemonic, not a model. What it gets right: risk should generally fall as the money's horizon shortens. What it gets wrong:
- It ignores everything except age — job stability, other income, a pension, property, dependants, whether you have thirty years of retirement still to fund.
- It assumes a single pot with a single horizon.
- Its constants are arbitrary, and were chosen in different interest-rate environments.
Target-date funds implement a version of this professionally, adjusting the mix automatically as a date approaches. For someone who does not want to manage an allocation, a single low-cost target-date or multi-asset fund is a perfectly reasonable answer — check its expense ratio and its glide path.
Diversifying within each class
- Across companies and sectors: a broad index fund does this by construction.
- Across countries: concentrating in your home market is the most common unforced error. Domestic markets can underperform for decades, and your salary and property are already exposed to your home economy.
- Across bond types: government versus corporate, and short versus long duration, behave very differently when rates move.
- Currency: if you invest internationally, part of your return is exchange-rate movement. Some funds hedge this; decide deliberately rather than by accident.
Adding a fifth equity fund is usually not diversification. Adding a different asset class, or a different country, is.
Rebalancing
Markets pull your allocation off target: after a strong equity run, a 60/40 portfolio might be 75/25 — carrying much more risk than you chose. Rebalancing sells some of what grew and buys what lagged, restoring the intended mix.
- By calendar: once a year is enough for most people.
- By threshold: when any class drifts more than about 5 percentage points from target.
- With new money first: direct contributions to the underweight class — the cheapest method, since it avoids selling entirely.
Rebalancing is a risk-control measure, not a return-boosting trick. In taxable accounts it can trigger tax, so prefer the new-money method there and check your own rules.
Common mistakes
- Choosing an allocation after a market move rather than before one. Decide when calm.
- Holding the emergency fund in the portfolio. It has a different job — see building an emergency fund.
- Confusing volatility with risk. For a 20-year horizon, the bigger risk is holding so much cash that inflation erodes it — see how inflation affects retirement.
- Ignoring costs. A well-chosen allocation in expensive funds can underperform a simpler one in cheap funds — see what an expense ratio means.
Sources and further reading
Primary sources are preferred: regulators, central banks, statistical agencies, tax authorities, index providers and original research. Links open on the publisher's own site; FinSage has no commercial relationship with any of them.
- U.S. SEC, Investor.gov — “Beginners' Guide to Asset Allocation, Diversification, and Rebalancing”.
- Dimson, Marsh & Staunton, Global Investment Returns Yearbook — long-run returns and drawdowns for equities, bonds and cash across many countries, and the evidence on home-market concentration.
- UK Financial Conduct Authority — guidance on assessing suitability, including capacity for loss (PDF).