Updated for the 2026-2027 CFA® Level I curriculum.
Index weighting methods decide how much each constituent stock affects an index's value and return. The same group of stocks can produce very different index behavior depending on how weights are assigned. After this note, you should be able to identify the four weighting methods tested at Level I, assign weights using each one, and explain how the choice of method changes an index's sensitivity to individual constituents.
Quick Answer
Index weighting methods determine each constituent's share of influence on an index. CFA Level I covers four methods: price weighting (weight based on share price), equal weighting (every constituent gets the same weight), market-capitalization weighting (weight based on total market value, often float-adjusted), and fundamental weighting (weight based on a financial measure such as earnings or book value). Each method reacts differently to price changes and constituent size.
Key Takeaways About Index Weighting Methods
Level I tests four weighting methods: price weighting, equal weighting, market-capitalization weighting, and fundamental weighting.
Price weighting sets a constituent's weight equal to its share price divided by the sum of all constituent prices.
Equal weighting assigns every constituent the same weight at each rebalancing date, regardless of price or company size.
Market-capitalization weighting sets weight equal to a constituent's market value divided by total index market value. Float-adjusted versions use only publicly tradable shares.
Fundamental weighting uses a financial measure, such as earnings, revenue, or book value, instead of market price.
A stock split changes weight under price weighting but has no effect on market-cap or fundamental weighting.
Equal-weighted indexes need more frequent rebalancing than market-cap-weighted indexes because price moves push weights away from equal shares.
What You Need to Know for CFA Level I
Identify the four weighting methods used to construct equity indexes.
Calculate a constituent's weight under price weighting, equal weighting, and market-cap weighting given basic price and share data.
Explain how a price change or corporate action affects a constituent's weight differently under each method.
Compare the strengths and weaknesses of each method without confusing weighting with security selection or rebalancing.
Recognize float-adjusted market-cap weighting as a variation that excludes closely held shares from the weight calculation.
The Major Weighting Methods You Need to Know
CFA Level I requires four weighting methods. Each one answers the same question in a different way: how much of the index does one constituent represent?
Price weighting. Weight is based on share price alone.
Equal weighting. Every constituent gets the same weight.
Market-capitalization weighting. Weight is based on total market value of outstanding shares, often float-adjusted.
Fundamental weighting. Weight is based on a financial measure that has no direct link to market price.
Knowing these four names is not enough for the exam. You need to know what drives the weight in each case, because that driver is what a question will test.
How Each Method Assigns Constituent Weights
Price Weighting
Where:
= price of constituent
= sum of all constituent prices
Weight depends only on price per share. A $200 stock gets twice the weight of a $100 stock, no matter how many shares each company has outstanding. A stock split cuts the price and the weight, even though nothing about the company's value has changed. This is a structural quirk of price weighting, not a market event.
Equal Weighting
Where:
= the number of constituents in the index.
Every constituent starts with the same weight. Because prices move daily, actual weights drift away from equal shares almost immediately after a rebalancing date. Keeping the index close to equal weight requires frequent rebalancing, which is a key operational cost of this method.
Market-Capitalization Weighting
Where
- the number of shares outstanding for constituent (or float-adjusted shares, if used)
Weight depends on total market value, price times shares outstanding. Larger companies get larger weights. A float-adjusted version uses only shares available for public trading, excluding shares held by governments, founders, or other insiders that rarely trade. Most major cap-weighted benchmarks, including the S&P 500, use float adjustment.
Fundamental Weighting
Where:
= a fundamental measure for constituent , such as earnings, revenue, dividends, or book value.
Weight has no direct link to share price. A company with strong earnings gets a large weight even if its stock price is low, and a company with an inflated stock price does not automatically get a large weight. This breaks the connection between overvaluation and index weight that exists in price and market-cap weighting.
How Weighting Changes an Index's Sensitivity to Constituents
Weighting method decides which stocks move the index the most.
A price-weighted index is most sensitive to its highest-priced constituents, regardless of company size. A large price move in a high-priced stock swings the index even if that company is small by market value.
A market-cap-weighted index is most sensitive to its largest constituents by market value, regardless of share price. A large-cap stock with a low share price can still dominate the index.
An equal-weighted index spreads sensitivity evenly. A small company's return has the same impact on the index as a large company's return, which makes equal-weighted indexes behave more like small- and mid-cap benchmarks than their cap-weighted counterparts built from the same universe.
A fundamentally weighted index is most sensitive to companies that score highest on the chosen fundamental measure. This often creates a value tilt, since it can overweight companies with strong fundamentals trading at lower prices.
Comparing Strengths and Weaknesses
Method | Weight driver | Key strength | Key weakness |
|---|---|---|---|
Price weighting | Share price | Simple to calculate and understand | Arbitrary weights tied to price scale, distorted by stock splits |
Equal weighting | Equal share for each constituent | Removes size and price bias | Requires frequent rebalancing, higher turnover |
Market-cap weighting | Total market value | Reflects actual market structure, low turnover | Concentrates weight in largest companies, can overweight overpriced stocks |
Fundamental weighting | Financial metric (earnings, revenue, book value) | Breaks link between overvaluation and weight | Depends on the fundamental measure chosen, can lag price-driven trends |
Keep this comparison focused on weighting. Constituent selection (which stocks enter the index) and rebalancing or reconstitution (when and how weights or membership are updated) are separate decisions covered in the index construction note.
Worked Example
An index has three constituents.
Stock | Price | Shares outstanding | Market cap |
|---|---|---|---|
A | $20 | 10 million | $200 million |
B | $50 | 2 million | $100 million |
C | $80 | 1 million | $80 million |
Price weighting
Equal weighting
Market-capitalization weighting
Stock C has the highest price but the smallest market cap. Under price weighting, C dominates the index at 53.3%. Under market-cap weighting, C falls to 21.1%, and A, the largest company by market value, takes the largest weight at 52.6%. Equal weighting ignores both price and size, giving each stock the same 33.3% influence. The same three companies produce three different index structures depending on the weighting method.
Common Exam Traps
Confusing weighting rules with constituent selection
Weighting decides how much influence a constituent has once it is in the index. Selection decides which securities qualify for membership. These are separate steps in index construction.
Assuming all weighting methods respond the same way to a price change
A price increase raises weight under price weighting and market-cap weighting, but the size of the effect differs. Under equal weighting, weight only changes between rebalancing dates, not continuously with price.
Mixing index weighting with rebalancing or reconstitution
Weighting method is the rule for assigning weight. Rebalancing is the act of restoring weights to a target. Reconstitution is the act of changing index membership. A question may test whether you can tell these apart.
Describing a method without explaining what determines the weight
Naming "market-cap weighting" is not enough. You need to state that weight comes from price times shares outstanding (or float-adjusted shares), divided by total market value.
Practice Question
An index has three constituents:
Stock | Price | Shares outstanding | Market cap |
|---|---|---|---|
M | $100 | 1 million | $100 million |
N | $20 | 50 million | $1,000 million |
O | $10 | 20 million | $200 million |
Stock M has a high per-share price but a small market capitalization relative to the other constituents. Under which weighting method does Stock M have the greatest influence on index performance?
Price weighting
Equal weighting
Market-capitalization weighting
Correct Answer: A
Under equal weighting, M's weight is fixed at , or , the same as every other constituent.
Price weighting gives M the highest weight of the three methods because weight depends only on price per share, and M has the highest price in the group.
Option B: Equal weighting assigns identical weight (33.3%) to every constituent regardless of price or size. M's weight here is not maximized, it is simply equal to N and O.
Option C: Market-cap weighting ties weight to total market value. Because M has few shares outstanding, its market cap is the smallest of the three, giving it the lowest weight under this method, not the highest.
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FAQs About Index Weighting Methods
Is market-cap weighting the most common method for major equity indexes?
Yes, most widely followed benchmarks, including the S&P 500, use market-capitalization weighting, often with float adjustment applied to exclude closely held shares.
Does a stock split affect index weight?
It depends on the method. A split lowers weight under price weighting because price drops. It has no effect on market-cap or fundamental weighting because total market value and fundamentals are unchanged.
Is fundamental weighting the same as factor investing?
Fundamental weighting is one method that avoids linking weight to market price. Some fundamentally weighted indexes are marketed as factor or smart-beta strategies, but the LOS here only requires you to know how fundamental weighting assigns weight, not fund labeling.