Owning Twelve Australian Bank Shares Is Not Diversified
Diversification removes the risk specific to individual holdings — the company that fails, the sector that is disrupted, the country whose market stagnates. It does not remove market risk, and it is not achieved by owning many things from the same place. Australian retirement portfolios are frequently concentrated in three sectors of one market, with a long list of holdings that conceals it.
- The answer: Diversification reduces the risk that comes from individual holdings. Beyond a modest number of genuinely different exposures, adding more does very little.
- The trap: An Australian portfolio built for dividend yield is concentrated in banks and resources, however many individual shares it contains.
- The recommendation: Look at the exposures rather than the holdings — by country, by sector, and by asset class. That is where the concentration hides.
Where the AI summary above gets this wrong
"Diversify by holding at least 20 different shares to reduce your risk."
That's surface-true. Here's what it misses:
- Twenty shares from three sectors of one market is not diversified — What matters is how differently the holdings behave, not how many of them there are. Australian banks move together, however many you own.
- Diversification cannot remove market risk — A fall that affects the whole market affects a diversified portfolio too. That is what the cash buffer and the time horizon are for.
01 What it removes
Holding-specific risk is what diversification addresses: the company that fails, the property that cannot be let, the sector that is disrupted. Spreading across genuinely different exposures makes any single failure survivable.
The benefit accrues quickly and then flattens. Moving from three holdings to fifteen removes most of the specific risk; moving from fifteen to fifty removes very little more, provided the fifteen were genuinely different.
That is why an index fund does the job so efficiently. It is not that indexing is clever — it is that owning the whole market is the cheapest way to hold many genuinely different exposures at once, at the fee levels described in the investment costs post.
02 What it cannot remove
Market risk survives diversification. A fall that affects the whole equity market affects every equity portfolio, and no amount of spreading within equities changes that.
The tools for market risk are different: time horizon, the cash buffer that removes forced selling, and the Age Pension floor underneath an Australian household. Those are covered in the sequence risk reference.
Diversifying across asset classes — equities, fixed interest, property, cash — helps because they do not all fall together. That is a different kind of diversification from spreading across shares, and it is the one retirement portfolios most often underuse.
Source: ASIC Moneysmart — Shares
03 Where Australian portfolios concentrate
Home bias is the first. Australian investors hold far more domestic equity than the country's share of global markets would suggest, encouraged by franking credits and by familiarity.
Sector concentration is the second and follows from the first. The Australian market is dominated by financials and resources, so a domestic portfolio is a bet on those two sectors whether or not that was intended.
Property is the third, and it is the largest. A household with a home and an investment property has most of its wealth in Australian residential real estate before any share portfolio is considered, which is the point made in the property versus super post.
Shows: the share of a household's wealth in a single asset class or market, counting the home and any investment property alongside the portfolio. Ignores: correlations between the exposures, the difference between the home as a place to live and as an investment, and debt against any of it.
Add the house to the portfolio before deciding whether you are diversified. Most Australian households have the great majority of their wealth in residential property in one city, and then worry about whether their share portfolio has enough line items in it. The concentration is real and it is not in the share portfolio.
FAQ
What is diversification?
Holding genuinely different exposures so that no single failure is damaging. It removes holding-specific risk and cannot remove market risk, and the benefit flattens quickly once the exposures are genuinely different.
Is owning twenty Australian shares diversified?
Not necessarily. The Australian market is dominated by financials and resources, so twenty holdings can be a concentrated bet on two sectors of one market. Look at the exposures rather than the number of line items.
What can diversification not protect against?
A fall affecting the whole market. The tools for that are a long horizon, a cash buffer that removes forced selling, and — for an Australian household — the Age Pension floor.
Sources
Regulator references
- ASIC Moneysmart — Choose your investments · ASIC Moneysmart · 2026Choosing investments: risk, diversification and time horizon.Last verified: 2026-09-07
- ASIC Moneysmart — Shares · ASIC Moneysmart · 2026How shares work, the returns they pay, and the risks of holding them.Last verified: 2026-09-07
Calculator unit tests · the assertions this page's worked example is checked against, and their last result
Changelog
- 2026-09-07 — initial publish (new format)
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Jordan Reeves
Founder of Talk Through Wealth. A software engineer for over a decade before turning to retirement planning, Jordan built the projection engine after watching family members get fragmented, country-by-country advice that never reconciled. He writes about retirement the way the engine computes it: month-by-month, lifetime-long, and skeptical of any rule of thumb that hasn't been run through the math.