--- title: "TOPIX Core30: Methodology" description: "TOPIX Core30 is maintained by JPX/Nikkei and covers Japanese blue-chip equity benchmark. How it selects and weights its constituents, and what it measures." canonical: https://www.getswoopr.com/stocks/indexes/topix-core30/ source: "Swoopr Investment: https://www.getswoopr.com" --- # TOPIX Core30: What It Measures and How It Is Built ## Direct Answer > The TOPIX Core30 is a rule-based measurement of Japanese blue-chip equity benchmark, maintained by JPX/Nikkei. 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 TOPIX Core30 covers Japanese blue-chip equity benchmark, within the Japan market. JPX/Nikkei 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 30 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 Free float adjusted market capitalization weighted, using the same free float weight that TOPIX uses and the market cap weighting formula in the Index Calculation Guidebook. Price return and total return versions are calculated. 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 Chosen only from the issues selected in the TOPIX periodic review. The 30 names come in two steps of 15: the first takes the largest by market cap from the 90 most traded issues, and the second takes the largest from the TOPIX Selected Issues and Core30 constituents as of the base date that are both in the 90 most traded and in the 40 largest by market cap, with any shortfall filled in trading value order from the 90 most traded. 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. ## When the membership is revised Reviewed annually in October with a base date of the last business day of August. Results are published on the fifth business day of October and applied from the last business day of October. Between reviews a newly listed issue joins Core30 only if it ranks in the top 20 by market cap and the top 90 by trading value, and delistings are not backfilled until the next October review. 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 Core30 is not simply the 30 largest companies: it needs size and trading activity together, so every member must sit among the 90 most traded issues even when a larger but thinly traded company exists. ## References - [JPX/Nikkei: JPX Market Innovation and Research TSE Index Guidebook (TOPIX New Index Series, Size based TOPIX Sub Indices), November 2, 2026 edition published July 24, 2026](https://www.jpx.co.jp/english/markets/indices/topix/tvdivq00000030ne-att/e_cal2_12_size_rev2.pdf), as published 2026. Every rule described on this page is taken from this document. ## Current TOPIX Core30 constituents JPX/Nikkei publishes and licenses the TOPIX Core30 constituent list. Swoopr does not republish it here. The provider's own page is the authoritative source for current membership and weights. [JPX/Nikkei: official TOPIX Core30 page](https://www.jpx.co.jp/english/markets/indices/index.html) ## Related reading - [All stock market indexes](https://www.getswoopr.com/stocks/indexes/): how indexes are built, weighted and revised. - [Asia-Pacific indexes](https://www.getswoopr.com/stocks/indexes/asia-pacific/): 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 TOPIX Core30? JPX/Nikkei maintains the TOPIX Core30 and publishes the methodology document that defines its eligibility and weighting rules. ### What does the TOPIX Core30 measure? It measures Japanese blue-chip equity benchmark. 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 TOPIX Core30 constituents? JPX/Nikkei 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.