After-Cost Index Decision Rule
Compare active investing with the whole market only after every investor cost
- Difficulty
- Easy
- Time to result
- ~days to results
- Steps
- 6
- Confidence
- 99%
Malkiel's decision rule begins with market arithmetic. Every outstanding share must be owned, so active investors collectively hold the same market represented by the index. Before costs, winners and losers balance: one investor's excess return requires another's shortfall. The comparison changes after costs. An index fund holds the whole market for a very small fee, while active management subtracts a larger management charge, bid-ask spreads, market impact, and often taxable capital-gains distributions. The investor should therefore compare net outcomes rather than manager stories or gross returns. Persistence is a second check: Malkiel cites SPIVA findings that most active mutual funds underperform and that one year's outperformers are not reliably the next year's winners. When a claimed edge does not survive costs and persistence testing, broad low-cost indexing is the default.
Origin
Malkiel advocated publicly for index funds in 1973, three years before Jack Bogle launched the first Vanguard index fund.
Core principles
- 01All securities are held by someone, so active investors collectively hold the market.
- 02One active investor's outperformance requires another's underperformance before costs.
- 03Fees transfer returns from the investor to the service provider.
- 04Trading adds spreads, market impact, and tax costs.
- 05Low-cost indexing can deliver above-average after-cost results without selecting winners.
How to run it
- 1
Define the market alternative
Choose a broad, investable index covering the same securities and risk exposure as the active option. This becomes the relevant baseline.
Pro tip Match geography and asset class before comparing returns.
Watch out An unsuitable benchmark can make ordinary exposure look like manager skill.
- 2
Apply the zero-sum baseline
Recognize that active investors collectively own the market. Treat aggregate active performance before costs as the market return, with winners balanced by losers.
Pro tip Evaluate the whole active group before focusing on a celebrated winner.
Watch out Visible winners do not reveal the probability of selecting them in advance.
- 3
Subtract explicit fees
Deduct management, advisory, and product charges from the active and indexed alternatives. Compare the annual difference and its long-run compounding effect.
Pro tip Express every charge in basis points for a like-for-like comparison.
Watch out A one-percentage-point annual fee compounds into a large lifetime transfer.
- 4
Subtract hidden trading costs
Account for bid-ask spreads, market impact, turnover, and taxable distributions. Use after-tax results when the investment sits in a taxable account.
Pro tip Inspect turnover and capital-gains distributions, not just the headline expense ratio.
Watch out Trading is not free even when commissions appear to be zero.
- 5
Test persistence
Check whether active outperformance repeats across periods and survives fees. Avoid selecting a manager solely because of one strong year.
Pro tip Compare the identity of outperformers across consecutive years.
Watch out Past winners can revert while still attracting money at the worst time.
- 6
Choose the net-return default
Use the low-cost index when the active option lacks a durable, after-cost advantage. Treat indexing as an above-average net strategy rather than a promise of average investor results.
Pro tip Revisit the decision if fees, taxes, or the available products materially change.
Watch out Do not pay more merely for the possibility of gross outperformance.
In the wild
Malkiel contrasts an active manager charging roughly one percent annually with an index ETF charging only four or five basis points. The active fund also trades more and may distribute taxable gains.
→ The cost difference accrues to the index investor unless the active manager produces a persistent gross advantage large enough to overcome it.
Malkiel says the annual SPIVA report repeatedly found roughly two thirds of active mutual funds underperforming the index, while the minority outperforming in one year was not the same minority in the next.
→ The evidence weakened both the average active case and the prospect of selecting a repeat winner beforehand.
Common mistakes
Comparing gross returns
The investor receives returns only after management, trading, and tax costs have been removed.
Selecting last year's winner
Malkiel notes that the funds outperforming in one year are not reliably the same funds outperforming in the next.
Calling indexing mediocre
Because active investors bear higher costs, a very low-cost market return can rank above the average investor's net result.
Is it for you?
Best for
It is best for choosing between active funds, advisers, ETFs, and broad index funds.
Not ideal for
It is not designed to select a specific security or evaluate nonfinancial goals such as voting control.
From the transcript
“the lower the fee I pay to the purveyor of the investment service, the more that's going to be for me.”
“investing has to be a zero sum game.”
“After fees, they're going to underperform.”
From the episode
Interview With Burt Malkiel: Masters in Business (Audio)
Burt Malkiel