Direct Answer
The S&P/NZX 20 is a rule-based measurement of top 20 companies listed on the New Zealand Exchange by float-adjusted market cap, maintained by S&P Dow Jones Indices/NZX. 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 S&P/NZX 20 covers top 20 companies listed on the New Zealand Exchange by float-adjusted market cap, within the New Zealand market. S&P Dow Jones Indices/NZX 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
Weighted by float-adjusted market capitalization with a single stock cap of 15%, applied at each quarterly rebalancing using prices from the Wednesday before the second Friday of the month.
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
Measures 20 of the largest and most liquid securities on the NZX Main Board. A stock must have absolute liquidity above 3.5% over the six month review period. It is the underlying index for NZX futures and options.
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
Rebalanced quarterly in March, June, September and December, effective after the close on the third Friday. A non-member is added at rank 16 or higher, and a member is removed at rank 24 or lower.
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
Cap shares are assigned from prices seven trading days before the rebalancing, so the actual weight of a capped stock at the rebalancing can differ from 15% because of market movements.
References
- S&P Dow Jones Indices/NZX: S&P Dow Jones Indices, S&P/NZX New Zealand Indices Methodology, as published 2025. Every rule described on this page is taken from this document.
Current S&P/NZX 20 constituents
S&P Dow Jones Indices/NZX publishes and licenses the S&P/NZX 20 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 S&P/NZX 20?
S&P Dow Jones Indices/NZX maintains the S&P/NZX 20 and publishes the methodology document that defines its eligibility and weighting rules.
What does the S&P/NZX 20 measure?
It measures top 20 companies listed on the New Zealand Exchange by float-adjusted market cap. 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 S&P/NZX 20 constituents?
S&P Dow Jones Indices/NZX publishes the current constituent list. Swoopr does not republish it, because index providers license constituent data and Swoopr holds no such licence.