Level III Core · Overview of Equity Portfolio Management

Active Share and Active Management Decisions Explained

Updated 8 October 2026 · Fact-checked

Active share measures how much a portfolio's holdings differ from its benchmark: Active share = ½ × Σ |wp − wb|. Tracking risk measures how much the return difference varies over time. Low on both suggests closet indexing. High active share with low tracking risk or the reverse points to different kinds of bets.

Understand Active Share and Active Management Decisions

Active share answers a simple question: how different are the portfolio's holdings from the benchmark's holdings? It looks at weights only, at one date. A fund that holds exactly the benchmark has an active share of 0%. A fund that holds no benchmark securities has an active share of 100%.

Tracking risk (also called tracking error) answers a different question: how much does the portfolio's return differ from the benchmark's return, and how variable is that difference? It is the standard deviation of active returns, where active return = portfolio return − benchmark return. It is measured from return history, not from holdings.

The two measures capture different things. Active share shows how much of the portfolio is stock selection away from the benchmark. Tracking risk shows how much the benchmark-relative return moves. A portfolio can have high active share but modest tracking risk if its bets are diversified and offset each other. It can also have lower active share but high tracking risk if it takes large factor or sector bets, such as a big tilt to one style.

A closet indexer charges active fees but holds a portfolio very close to the benchmark. It has low active share and low tracking risk. The manager says the approach is active, but the client pays for little more than an index. Look at both measures together, and compare them with the fees and the stated approach.

The usual reading is this: a stock picker with a concentrated portfolio shows high active share and often higher tracking risk. A diversified stock picker shows high active share and moderate tracking risk. A factor or sector bettor shows lower active share but high tracking risk. A closet indexer shows low on both. Active share does not prove skill. It only shows the manager is different from the benchmark. Whether that difference adds value depends on the active return after fees.

Key rules to remember

Active share: Active share = ½ × Σ |wp,i − wb,i|; Sum over all securities held by the portfolio or the benchmark. Weights are portfolio and benchmark weights. Result ranges from 0% to 100% for long-only portfolios.
Active share (overweights only): Active share = Σ of positive (wp,i − wb,i) = Σ of negative differences in absolute value; This holds when the portfolio weights and the benchmark weights each sum to 100% (long-only, no cash, no leverage). Then overweights equal underweights, so you can sum one side only.
Active return: Active return = Rp − Rb; Return of the portfolio minus return of the benchmark for the same period.
Tracking risk (tracking error): Tracking risk = standard deviation of (Rp − Rb); Use the sample standard deviation of periodic active returns, then annualise if asked (monthly × √12).
Information ratio: IR = average active return ÷ tracking risk; Active return per unit of tracking risk. Use the same time basis for both.

How to solve Active Share and Active Management Decisions questions

Use this order for any question on active share, tracking risk or whether a manager is really active.

1Identify what is asked: a calculation (active share, tracking risk, IR) or a judgement (is the manager truly active, is it closet indexing).
2For active share, line up each security's portfolio weight and benchmark weight. Treat a missing holding as a weight of 0%.
3Take the absolute difference for each security, sum them, and multiply by ½. Or sum the overweights only if the portfolio is long-only and fully invested.
4For tracking risk, compute the active return for each period, then take the standard deviation of those active returns. Annualise only if asked.
5Read the two numbers together. Low active share and low tracking risk suggests closet indexing. High active share suggests stock-specific bets. High tracking risk with lower active share suggests factor or sector bets.
6Link the result to fees and the stated approach. Ask if the cost is justified by the degree of activeness.
7Answer the command word. If asked to justify, give the number, then the conclusion, then one reason. Show the calculation.

Quickest way: Overweight-only shortcut for active share

When to use it: Long-only portfolio and benchmark, both fully invested, with a short list of positions in a vignette.

Write portfolio weight minus benchmark weight for each holding.
Add only the positive differences. Include holdings the benchmark does not own as positive.
That sum is the active share. Check it by adding the negatives in absolute value; the two should match.
State the conclusion in one line: for example, an active share of 30% is low for a manager claiming a concentrated stock-picking style.

Common mistakes in Active Share and Active Management Decisions

Forgetting the ½ in the active share formula.
Students sum absolute differences and stop, because the sum looks like a finished answer.
Fix: Check the range. Active share cannot exceed 100% for long-only portfolios. If your sum is 80% from overweights and underweights combined, halve it to 40%.
Treating active share and tracking risk as the same thing.
Both measure difference from the benchmark, so they sound alike.
Fix: Active share uses holdings weights at a point in time. Tracking risk uses the standard deviation of return differences over time.
Leaving out securities the benchmark holds but the portfolio does not.
Students only list the portfolio's holdings.
Fix: Include every security in either list. A zero holding still creates an underweight equal to its benchmark weight.
Concluding that high active share means the manager has skill.
High active share is read as good.
Fix: High active share means different from the benchmark. Skill shows up in net active return and the information ratio, not in active share alone.
Calling any low tracking risk fund a closet indexer.
Low tracking risk is read in isolation.
Fix: Check active share too. A diversified stock picker can have high active share and moderate tracking risk. A closet indexer has both low.
Using the population formula or wrong time basis for tracking risk.
Rushing, and mixing monthly active returns with annual figures.
Fix: Use the sample standard deviation of periodic active returns and annualise (monthly × √12) before dividing into an annual active return.

Worked examples

Example 1

A long-only portfolio and its benchmark hold four stocks. Portfolio weights: A 40%, B 30%, C 20%, D 10%. Benchmark weights: A 25%, B 25%, C 25%, D 25%. Calculate the active share and state what it suggests about a manager who claims to be a high-conviction stock picker.

Show the solution

Differences (portfolio − benchmark): A +15%, B +5%, C −5%, D −15%.
Sum of absolute differences = 15 + 5 + 5 + 15 = 40%.
Active share = ½ × 40% = 20%.
Check with overweights only: 15% + 5% = 20%. It matches.

Answer: Active share is 20%. This is low for a manager claiming high-conviction stock picking, because 80% of the portfolio overlaps with the benchmark. The claim is not supported by holdings.

Example 2

A fund's monthly active returns over four months are +0.5%, −0.3%, +0.1%, and +0.3%. (Four months is used only to keep the arithmetic short; a real estimate needs a longer history.) Using the sample standard deviation, calculate the annualised tracking risk and the information ratio, with the average active return annualised by multiplying the monthly mean by 12.

Show the solution

Mean monthly active return = (0.5 − 0.3 + 0.1 + 0.3) ÷ 4 = 0.6 ÷ 4 = 0.15%.
Annualised average active return = 0.15% × 12 = 1.8%.
Deviations from the mean: +0.35, −0.45, −0.05, +0.15.
Squared deviations: 0.1225, 0.2025, 0.0025, 0.0225. Sum = 0.35.
Sample variance = 0.35 ÷ 3 = 0.11667. Monthly standard deviation = √0.11667 = 0.3416%.
Annualised tracking risk = 0.3416% × √12 = 0.3416 × 3.4641 = 1.183%, about 1.18%.
Information ratio = 1.8% ÷ 1.183% = 1.52.

Answer: Annualised tracking risk is about 1.18%. The information ratio is about 1.52.

Exam tips

Read the command word. 'Calculate' needs the number with working. 'Justify' or 'explain' needs a conclusion plus a reason tied to the data.
Show the weight differences line by line. A correct final number earns full credit, but a visible method protects you if you slip on one weight.
When asked whether a manager is truly active, quote both active share and tracking risk, then compare to the manager's stated style and fees.
In item sets, check whether the options mix up active share with tracking risk. Eliminate any option that defines active share using return volatility.
Sanity check: long-only active share must lie between 0% and 100%. If you get more, you missed the ½.

Active Share and Active Management Decisions in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Active Share and Active Management Decisions: frequently asked questions

What is the active share formula for CFA Level III?

Active share = ½ × Σ |wp − wb|, summed over all securities in the portfolio or the benchmark. It shows the share of the portfolio that differs from the benchmark. For a long-only portfolio the result lies between 0% and 100%.

What is the difference between active share and tracking risk?

Active share compares holdings weights with benchmark weights at a point in time. Tracking risk is the standard deviation of the return difference between portfolio and benchmark over time. A portfolio can score differently on each, so read them together.

How do you spot closet indexing?

A closet indexer has low active share and low tracking risk, yet charges active management fees. Its holdings and returns stay close to the benchmark. The client pays for active management but receives something close to an index.

Does high active share mean a better manager?

No. It only shows the portfolio differs from the benchmark. The manager may add or lose value. Judge skill by net active return, the information ratio and consistency over time.