--- title: "NSE 20 Share Index: Methodology" description: "NSE 20 Share Index is maintained by Nairobi Securities Exchange and covers top 20 companies listed on the Nairobi Securities Exchange by market activity." canonical: https://www.getswoopr.com/stocks/indexes/nse-20/ source: "Swoopr Investment: https://www.getswoopr.com" --- # NSE 20 Share Index: What It Measures and How It Is Built ## Direct Answer > The NSE 20 Share Index is a rule-based measurement of top 20 companies listed on the Nairobi Securities Exchange by market activity, maintained by Nairobi Securities Exchange. Like every index it owns nothing: it is a number produced by applying a published weighting formula to a selected list of companies, revised on a schedule the provider sets. ## What this index covers The NSE 20 Share Index covers top 20 companies listed on the Nairobi Securities Exchange by market activity, within the Kenya market. Nairobi Securities Exchange defines which securities are eligible, how they are selected from that pool, and how much each one contributes to the published number. The name states a target of 20 companies. A target is not a guarantee of the exact count on any given day: corporate actions, dual share classes and pending additions all move the real number around it. ## How constituents are weighted The ground rules call it a price weighted index but give the formula of an equal weighted geometric mean: the 20th root of the product of each stock's price relative to the prior day, multiplied by the previous index level. The daily price is the volume weighted average price, or the last trade if none occurred. The weighting method is the single biggest driver of how an index behaves. Two indexes covering the same market can diverge for years purely because they weight differently, which is why comparing index levels without knowing the method tells you very little. ## What qualifies for inclusion Primary listing on the NSE, at least 20% of shares quoted, a minimum market capitalisation of KES 20 million, and ideally a blue chip company with a strong profit and dividend record. Eligibility rules are the part of an index most readers never look at and the part that decides what it can possibly measure. A screen that excludes a whole sector, or admits only one listing venue, shapes the result far more than any day of trading does. ## How long a listing must exist first A company must have been continuously quoted on the NSE for at least one year. A seasoning rule is why a large new listing does not appear in an index the week it starts trading. It is a deliberate lag, and it means an index can under-represent a fast-growing part of the market for months at a time. ## When the membership is revised The Trading Committee, acting as Index Management Committee, reviews constituents semi-annually. Securities are scored on market capitalisation (40%), shares traded (30%), deals (20%) and turnover (10%), then ranked by market capitalisation; a constituent ranked 21st or lower qualifies for removal and a reserve list of five is published. Reconstitution is the one date an index changes shape by design rather than by price. Funds tracking it have to trade toward the new membership, which is why the schedule matters to anyone holding the tracker rather than only to the provider. ## The rule that surprises people Although the document describes the index as price weighted, the geometric mean gives every one of the 20 stocks the same influence on percentage moves regardless of company size or share price. ## References - [Nairobi Securities Exchange: Nairobi Securities Exchange, Ground Rules for Generation of NSE 20 Share Index v1.6](https://www.nse.co.ke/wp-content/uploads/groundrules-nse-20-share-index_-v1.6.pdf), as published 2025. Every rule described on this page is taken from this document. ## Current NSE 20 Share Index constituents Nairobi Securities Exchange publishes and licenses the NSE 20 Share Index constituent list. Swoopr does not republish it here. The provider's own page is the authoritative source for current membership and weights. [Nairobi Securities Exchange: official NSE 20 Share Index page](https://www.jse.co.za/services/market-data/indices) ## Related reading - [All stock market indexes](https://www.getswoopr.com/stocks/indexes/): how indexes are built, weighted and revised. - [Emerging Markets indexes](https://www.getswoopr.com/stocks/indexes/emerging-markets/): others covering the same region. - [Index concentration](https://www.getswoopr.com/technical-analysis/market-concentration/index-concentration/): measuring how much of an index sits in its largest holdings. - [Index rebalancing and inclusion effects](https://www.getswoopr.com/stocks/corporate-actions-catalysts/index-rebalancing-and-inclusion-effects/): what happens to a stock when index membership changes. ## Frequently Asked Questions ### Who maintains the NSE 20 Share Index? Nairobi Securities Exchange maintains the NSE 20 Share Index and publishes the methodology document that defines its eligibility and weighting rules. ### What does the NSE 20 Share Index measure? It measures top 20 companies listed on the Nairobi Securities Exchange by market activity. The index is a calculated number applying a weighting formula to a selected list of companies, and it holds nothing itself. ### Where can I see the current NSE 20 Share Index constituents? Nairobi Securities Exchange publishes the current constituent list. Swoopr does not republish it, because index providers license constituent data and Swoopr holds no such licence. ## About the author The [Swoopr Editorial Team](https://www.getswoopr.com/authors/swoopr-editorial-team/) writes Swoopr Investment's educational library, covering market structure, analysis methods and the mechanics behind the numbers investors read every day. Our [editorial policy](https://www.getswoopr.com/legal/editorial-policy/) and [corrections policy](https://www.getswoopr.com/legal/corrections-policy/) set out how this content is produced, reviewed and fixed when it is wrong.