Capitalization-Weighted Index¶

A capitalization-weighted (or cap-weighted) index, also called a market-value-weighted index is a stock market index whose components are weighted according to the total market value of their outstanding shares.

Version: v1 · 2026-09-28 · History
Domain-specific #: 8336
Domain group: Social Sciences
Origin domain: Economics & Finance
Subdomains: Financial Indices, Portfolio Theory → Economics & Finance

Core Idea¶

Capitalization-Weighted Index is treated here as the recurring computer science and information systems identity summarized by this source-grounded definition: A capitalization-weighted (or cap-weighted) index, also called a market-value-weighted index is a stock market index whose components are weighted according to the total market value of their outstanding shares. A capitalization-weighted (or cap-weighted) index, also called a market-value-weighted index is a stock market index whose components are weighted according to the total market value of their outstanding shares. Every day an individual stock's price changes and thereby changes a stock index's value.

How would you explain it like I'm…

Big Companies Count More

A stock market index is one number that shows how a group of companies is doing. In a capitalization-weighted index, bigger companies count more, like a scale where heavy things tip it more than light things. So when a giant company's value moves, the index moves a lot; when a tiny company's value moves, the index barely budges.

The Market-Value Scoreboard

A stock market index is a single number that tracks a group of companies' shares. In a capitalization-weighted index, each company's share of the index depends on its market value: its share price times the number of shares that exist. So a huge company counts much more than a small one. When a big company's share price changes, the index changes a lot, and when a small company's price changes, the index changes only a little. Because prices and share counts keep changing, each company's weight in the index keeps shifting too.

Market-Value-Weighted Index

A capitalization-weighted, or market-value-weighted, index is a stock market index whose components are weighted by the total market value of their outstanding shares. A company's market value is its share price multiplied by its number of outstanding shares. When one stock's price changes, its effect on the index is proportional to that company's overall market value. That makes large companies dominate the index's movement. Other kinds of indices weight their components by different ratios, so the cap-weighting rule is what defines this type.

A capitalization-weighted index weights each constituent by its market capitalization, the share price times the number of outstanding shares. The index value therefore moves with the aggregate market value of its components, and a given percentage change in one stock's price affects the index in proportion to that company's share of total capitalization. Weights are not fixed: they drift automatically as prices change and are adjusted when the number of outstanding shares changes. As an example of an index built on all traded securities of an exchange, the NYSE Amex Composite (XAX) includes stocks and ADRs, with each component's weight shifting with its price and shares outstanding. Other index designs use different weighting ratios, and a positive case of this concept must actually weight by total market value of outstanding shares, not merely be a well-known index.

Scope of Application¶

Other types of indices. An index may also be classified according to the method used to determine its price.
Free-float weighting. With this method a float factor is assigned to each stock to account for the proportion of outstanding shares that are held by the general public, as opposed to "closely held".
Free-float weighting. In other words, the number of shares used for calculation is the number of shares "floating", rather than outstanding.
Documented setting. In other types of indices, different ratios are used.
Free-float weighting. A common version of capitalization weighting is the free-float or public-float weighting.

Clarity¶

A clear use of Capitalization-Weighted Index names the carrier, the operative relation, and the conditions under which the source treats the identity as present. The minimal definition is A capitalization-weighted (or cap-weighted) index, also called a market-value-weighted index is a stock market index whose components are weighted according to the total market value of their outstanding shares.

Manages Complexity¶

Capitalization-Weighted Index compresses multiple computer science and information systems details into a stable diagnostic relation. The source shows both the central mechanism—in a fundamentally weighted index, stocks are weighted by fundamental factors like sales or book value.—and the practical consequence—in other words, the number of shares used for calculation is the number of shares "floating", rather than outstanding.

Abstract Reasoning¶

Type the carrier. Identify the computer science and information systems entities to which the claim applies.
State the relation. Use the source-grounded identity: A capitalization-weighted (or cap-weighted) index, also called a market-value-weighted index is a stock market index whose components are weighted according to the total market value of their outstanding shares.
Check operation and conditions. For example, if 15% of shares of a stock are closely held, and the other 85% are publicly held, the float factor will be 0.85, by which the.

Knowledge Transfer¶

Within the home domain. Knowledge about Capitalization-Weighted Index transfers literally when a new case preserves the same carrier type, relation, and recognition test. An index may also be classified according to the method used to determine its price. With this method a float factor is assigned to each stock to account for the proportion of outstanding shares that are held by the general public, as opposed to "closely held" shares owned by the government, royalty, or company insiders. Beyond the home domain. No canonical parent is asserted for Capitalization-Weighted Index.

Relationships to Other Abstractions¶

Current abstraction Capitalization-Weighted Index Domain-specific

Parents (1) — more general patterns this builds on

Capitalization-Weighted Index is a kind of, typical Aggregation Prime

A cap-weighted index deliberately collapses many stock prices into one summary number, weighted by market value.

Hierarchy path (1) — routes to 1 parentless root

Capitalization-Weighted Index → Aggregation → Micro Macro Linkage

Neighborhood in Abstraction Space¶

Capitalization-Weighted Index sits in a moderately populated region (53^rd percentile for distinctiveness): it has near-neighbors but no dense thicket of look-alikes.

Family — Financial Indices & Trading Indicators (15 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-08