Direct Answer
The Nikkei 500 Stock Average is a rule-based measurement of Japanese broad 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 Nikkei 500 Stock Average covers Japanese broad 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 500 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
Same method as the Nikkei 225: constituent prices are multiplied by a price adjustment factor, summed and divided by a divisor, so it is a price average rather than a market value index. A new constituent normally gets a factor of 1, and the divisor is corrected for membership changes and price changes not caused by the market. Industry sub-indexes are calculated the same way.
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
Ordinary domestic parent shares listed on the Tokyo Stock Exchange Prime Market, excluding ETFs, REITs, preferred contribution securities and similar non-ordinary shares. Each year every Prime stock is ranked on annual trading volume, annual trading value and year end market capitalization. The three ranks are summed and re-ranked, the yearly results for the last three years are summed and ranked again, and the top 500 are selected.
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
Constituents are reviewed once a year at the beginning of April using rankings for the three preceding years. A delisting designation, a merger or share transfer delisting, or a move off the Prime Market triggers an extraordinary replacement, normally by the highest ranked non-member from the latest review, effective five business days after a delisting designation or on the event date for restructurings.
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
Membership is rebuilt from scratch each year: the guidebook states that the previous year's constituents are not consulted in selection, so there is no buffer for incumbents. Nikkei also calculates averages for each of its 36 mid level industries from the same 500 stocks.
References
- JPX/Nikkei: Nikkei Inc. Nikkei 500 Stock Average Calculation Guidelines (Japanese language index guidebook, July 24, 2025 version), as published 2025. Every rule described on this page is taken from this document.
Current Nikkei 500 Stock Average constituents
JPX/Nikkei publishes and licenses the Nikkei 500 Stock Average constituent list. Swoopr does not republish it here. The provider's own page is the authoritative source for current membership and weights.
Related reading
- All stock market indexes: how indexes are built, weighted and revised.
- Asia-Pacific indexes: others covering the same region.
- Index concentration: measuring how much of an index sits in its largest holdings.
- Index rebalancing and inclusion effects: what happens to a stock when index membership changes.
Frequently Asked Questions
Who maintains the Nikkei 500 Stock Average?
JPX/Nikkei maintains the Nikkei 500 Stock Average and publishes the methodology document that defines its eligibility and weighting rules.
What does the Nikkei 500 Stock Average measure?
It measures Japanese broad 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 Nikkei 500 Stock Average 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.