How a crypto index is built

A fund says it tracks "the crypto market". A dashboard shows a line labelled with an index's name. A vendor offers to sell you index values by API. All three are the same kind of object — a basket of assets chosen and weighted by a published rulebook — and every useful question about any of them is a question about the rulebook, not about crypto.

How it works

An index has two layers, and it helps to keep them apart.

The bottom layer is a price per asset. Somebody has to decide what bitcoin, ether or any other constituent is worth at a given second, which means choosing venues, weighting their trades and throwing out the bad prints. That layer has its own page here — where the bitcoin price actually comes from — and this page takes it as given. What matters for an index is only that every provider names the per-asset price it uses, and that the name can change: MarketVector replaced CCData's CCIX rates with BITA's real-time rates as the price source for its digital-asset indexes on 12 August 2026.

The top layer is the basket, and it is five decisions, each written down in the provider's methodology document:

1. Eligibility — which assets may be considered at all.
2. Venue vetting — which exchanges' data may count, for liquidity and for price.
3. Selection — how many assets, ranked by what, and how hard it is to fall out.
4. Weighting — by market capitalisation, and whether that is capped.
5. Maintenance — how often the list and the weights are refreshed, and what happens between refreshes.

Around those sits an administrator, which runs the calculation and answers for it; often a separate calculation agent, which computes the numbers; and a licence, which is what anybody who wants to use the result in a product signs. The rest of this page takes the five decisions in order, using four published rulebooks side by side: the CoinDesk 20 (CD20), the MarketVector Digital Assets 100 (MVDA) and its 25-asset sibling (MVDA25), the Nasdaq CME Crypto Index (NCI) and the FTSE Global Digital Asset Index Series.

Who is allowed in

Every rulebook starts by excluding things, and the exclusion lists are where the indexes differ most in spirit.

Assets that do not float. The CD20, the MVDA and the NCI all keep stablecoins out. The MVDA also drops wrapped tokens — "digital assets or cryptocurrency tokens that represent another token but exist on a different blockchain" — and the NCI requires "free-floating pricing", excluding anything pegged "through fiat or crypto collateralization, algorithmic strategy, or any other means". FTSE Russell does it one level down: its Digi50 indices take the constituents of the FTSE Digital Asset Total Cap Index "excluding" three stablecoin subsectors of Digital Asset Research's taxonomy. The ground rules do not say outright that the Total Cap index holds stablecoins; that is our inference from the carve-out, and its Top 20 indices, drawn from the same Total Cap index, carry no such carve-out.

Categories the provider does not want. The CD20 methodology, in its July 2026 version, excludes wrapped, pegged and staked assets, memecoins, privacy tokens, and gas tokens on chains that also have a separate governance or staking token. The MVDA25 has excluded meme and privacy tokens since 1 October 2023; the MVDA100 it is drawn from does not. The NCI reserves the right to exclude assets that "do not offer utility" — "assets inspired by memes or internet jokes" is its example — at the discretion of Nasdaq's Index Management Committee.

Securities. The CD20 excludes an asset meeting its policy document's definition of an unregistered security; the MVDA's universe is "excl. security tokens and financial instruments"; the NCI "will not include assets deemed to be securities by US regulators". Note the three different tests: a provider's own definition, a category label, and a regulator's view.

Custody. This is the rule that shows who an index is built for. Since the methodology's revision of 2 April 2025, a CD20 constituent must be supported by Coinbase Custody Trust Company. An NCI constituent must have been supported by at least one Nasdaq-approved "Core Custodian" for the whole period since the last reconstitution, because, in the methodology's words, funds "hardly have the technical expertise to safely self-custody digital assets". An asset can be large, liquid and entirely unobjectionable and still be out, because the custodian a fund would use does not hold it. FTSE Russell's vetting guide asks for "robust custody" too, but accepts hardware security modules or air-gapped software wallets as well as an approved custodian, and adds a test the others do not publish: the asset's code must be open source under a standard licence, in version control, with signed releases.

Listability. The NCI goes one step further. Since a rule change effective 30 October 2025, an asset must trade on a market that is a member of the Intermarket Surveillance Group, or underlie a futures contract that has been listed on a US designated contract market for at least six months, or — on an initial basis only — be at least 40% of the net assets of an ETF already listed on a US national securities exchange. The methodology says outright that these criteria "are intended to generally align with" Nasdaq's generic listing standards for commodity-based trust shares. FTSE Russell has an index built the same way: its Crypto US Listed Index takes only assets that meet the SEC's generic listing standards for crypto ETPs.

Read those two paragraphs together and one thing is plain. An index designed to be tracked by a US-listed fund is not a neutral sample of the market. It is the market restricted to what that fund could legally and operationally hold, and that is a feature of the product, not a flaw in it.

Which exchanges count

An index needs exchange data twice: once to measure liquidity when it picks constituents, and once to price them. Both uses depend on a list of approved venues, and each provider keeps its own.

FTSE Russell publishes its vetting rules in full, and they are the most concrete of the four. Digital Asset Research (DAR), the calculation agent for the per-asset prices FTSE's indexes use, sorts exchanges into two tiers. A Watchlist exchange must not restrict foreign investors, must name an identifiable leadership team, must be a centralised spot exchange, must deliver trade-level data with pair, price, volume and timestamp, and must report at least 5,000,000 USD of volume every day on average over the six months before each quarterly review. It must also pass data-science tests in each of the previous two quarters: trading that follows natural buy and sell patterns, trades at natural lot sizes, and two of three further checks on price, volume and order-book behaviour. The tests exist to catch reported volume that is not real trading.

A Participating exchange must meet all of that plus regulatory, governance and technical tests — licensed where it operates, KYC that verifies name, email, phone, government ID and bank account, no sanctions listing, a public fee schedule, no security breach in the last twelve months that lost more than 1% of total holdings, and no more than 24 cumulative hours of downtime in any quarter. The tiers matter because the assets are tiered on top of them. A constituent of the FTSE Global Digital Asset Index Series must be a "Benchmark Asset", which must be priced as "Tier 1", which means priced only from Participating exchanges — and trading on at least three of them to be classified for the first time. The exchange list is re-evaluated at each March, June, September and December month end. An exchange that fails is demoted a tier, onto a monthly-reviewed "Enhanced Eligibility" list or a penalty list, or disqualified, according to which criterion it failed.

Nasdaq calls them Core Exchanges, defines them in a separate guidelines document, and uses them directly in eligibility: an NCI constituent must have "active tradable markets listed on at least two Core Exchanges" for the whole period since the last reconstitution, and its liquidity is measured only on USD pairs on those exchanges.

MarketVector delegates. The MVDA25 requires every asset on its selection list to be listed on at least one exchange in BITA's Whitelisted Exchanges Report. Until the August 2026 revision the same role was played by CCData's Exchange Benchmark. The rule did not change; the list behind it did.

CoinDesk Indices describes venue criteria in categories rather than thresholds. The CD20 methodology itself only says that each constituent must support a CoinDesk Benchmark Rate, whose exchange-eligibility rules sit in a separate document not cited here. The clearest public statement we found is in a fund filing, and it is about a single-asset rate rather than the CD20: Grayscale's 10-K for its Ethereum Classic Trust, priced off the CoinDesk Ether Classic Price Index, lists market quality, security, legal and regulatory standing, KYC, data provision, transparency, team and "negative events", and requires a constituent platform to be licensed to serve customers in at least one of seven named jurisdictions — the United States, the United Kingdom, the EU under a MiCA passport, Hong Kong, Singapore, the UAE, or Gibraltar. The same filing says that index does not currently take data from OTC markets or derivatives platforms.

The practical upshot is that "the exchanges in the index" is not one list. Two indexes holding the same twenty assets can be measuring them on different venues, with different volume filters, and the difference shows up precisely when one exchange misbehaves.

How the weights are set

Selection and weighting are two separate passes, and the first one decides more than it looks.

Selecting: rank by what, and how sticky. The CD20 does not simply take the twenty largest coins. It first ranks everything eligible by 90-day median daily value traded on USD and USDC pairs, keeps the top 40 non-constituents and the top 50 current constituents, drops anything Coinbase Custody does not support, then ranks what is left by market capitalisation: the top 15 are in, current constituents inside the top 25 keep their places until there are 20, and anything still missing is filled from the next largest. The MVDA uses an 80–120 buffer: the top 80 by market cap are in, and the last 20 places go to existing constituents ranked 81 to 120. The MVDA25 ranks its candidates twice — once by market cap, once by one-month trading value — and sorts by the sum of the two ranks, so a large but thinly traded asset can lose to a smaller liquid one. The NCI has no fixed count at all: an asset needs 0.5% of the total market capitalisation of eligible assets to enter and is removed below 0.25%, and if that leaves the index under 75% of the eligible market, the next largest are added until it is not. FTSE sorts by cumulative circulating capitalisation into bands — large cap is the top 70%, with entry at 68% and exit at 72%.

Every one of those buffers exists for the same reason: an asset hovering at the boundary would otherwise be added and removed on alternate reviews, and each of those trips is a trade for every fund tracking the index.

Weighting: market cap, and then the question of caps. All of these indexes start from market capitalisation, and the NCI adds a subtlety worth knowing: it uses total supply to decide whether an asset is big enough to be selected, and circulating supply — as determined by CF Benchmarks, its calculation agent — to set its weight.

After that they split. The MVDA is uncapped: its cap factors are "fixed at 1", so its weights are the market's. The NCI weights by free-float market cap with no cap in the methodology. The CD20 caps its largest constituent at 30% and every other at 20%, redistributing the excess to the uncapped members in proportion to their size. The MVDA25 runs a three-level scheme: components above 4.5% (and at least the largest five) form a "Large-Weights" group capped at 50% in aggregate, with each member held between 5% and 20%, and everything else capped at 4.5%. FTSE runs its Top 20 index twice, once uncapped and once capped at 25% per asset.

The effect is that "a top-20 crypto index" can mean a portfolio in which bitcoin dominates or one in which it is held to less than a third, and the name will not tell you which. The cap is the single number most worth reading before comparing the performance of any two of them.

Two more details decide how a weight behaves between reviews. The CD20 fixes its weights on a "Weighting Reference Date" seven calendar days before the change takes effect, and states plainly that constituent weights "will drift with constituent price movements" between those two dates. And supply is frozen between reviews: the CD20 locks the circulating supply it used on that reference date, the MVDA does not adjust for changes in the amount outstanding during the month, and the NCI holds circulating supply fixed until the next rebalance, so a token unlock mid-quarter changes nothing until the calendar says it does.

When the list changes

Maintenance is two calendars, not one. A reconstitution changes which assets are in; a rebalance resets the weights of the ones already there. Some indexes do both on the same day. Each event has its own dates — a snapshot of the data, a public announcement, and the moment the change takes effect — and the gaps between them are published.

Between reviews the rules are asymmetric. The CD20 makes no additions between reconstitutions, and when a constituent is removed out of schedule it is not replaced: the count drops below twenty, the weight is shared out proportionally among the rest, and nothing is recapped. The NCI does not reconstitute or rebalance intra-quarter except to protect the index or in "exceptional events", with the Index Management Committee's approval.

Forks are handled in writing, and differently. When an MVDA constituent hard-forks, the new coin is added to the index for at least a day if it trades on a whitelisted exchange, and the criteria MarketVector says it takes into account include community support measured partly by Twitter followers, an accountable public developer, open source code, premine transparency and advance announcement of the fork. The NCI takes the opposite line: a coin from a fork or an airdrop is assessed under the same criteria as any other asset and is included only if it meets them.

The methodology itself changes. Every document cited here carries a change log, and the logs are busy. The CD20's runs from its first version on 11 January 2024 to a clarification of the gas-token definition on 7 July 2026, taking in the custody rule, a new divisor formula and the renaming of its price inputs to "CoinDesk Benchmark Rates" along the way. Nasdaq renamed its flagship from the Nasdaq Crypto Index to the Nasdaq CME Crypto Index on 20 January 2026, keeping the NCI ticker. MarketVector moved both its price source and its exchange list to BITA in August 2026. None of that is unusual; it is the normal life of a rulebook, and it is why "the methodology" is always a document with a date.

Who publishes them

A crypto index has up to three parties behind it, and they are often different companies. The owner holds the name and the rules. The administrator runs the benchmark and answers to a regulator, where there is one. The calculation agent computes the numbers. Knowing which is which tells you who can change the index and whom a licence is signed with.

• CoinDesk Indices owns the CoinDesk 20. Administration and calculation are done by its affiliate CC Data Limited, which the methodology describes as "an FCA regulated benchmark administrator" — the company whose data business now trades as CoinDesk Data. The index is calculated around the clock and its values are published on CoinDesk's index site, with REST and WebSocket access for subscribers.
• MarketVector Indexes GmbH owns the MarketVector Digital Assets family, which launched on 23 October 2017 and carried the "MVIS / CryptoCompare" name until 1 March 2023. The MarketVector trademark belongs to Van Eck Associates Corporation. Its index guides state that all its indexes qualify as non-significant benchmarks under the amended EU Benchmarks Regulation and so, from 1 January 2026, sit outside the regulation's direct scope — while MarketVector says it keeps applying the governance framework it built under it and the IOSCO principles.
• Nasdaq owns and administers the Nasdaq CME Crypto Index. CF Benchmarks calculates it, and the methodology names CME Group as a distribution channel for it alongside Nasdaq's own feeds.
• FTSE International, trading as FTSE Russell, is the benchmark administrator of the Global Digital Asset Index Series and calculates it. Digital Asset Research is the calculation agent for the per-asset prices underneath: DAR vets the exchanges and the assets, supplies the price feeds and advises on eligibility, and FTSE runs the index series on top.
• CF Benchmarks, besides calculating the NCI, administers the CME CF reference rates. Those are single-asset rates rather than baskets — the bitcoin one is what CME's bitcoin futures settle against — and they are taken apart on the bitcoin price page.

The data vendors in this catalogue sit on both sides of this. Coin Metrics sells its own CMBI indexes and reference rates, and Kaiko says its indices arm is a BMR-registered benchmark administrator — so the same company can be the one you license a price feed from and the one you license an index from, under two different agreements.

What it costs

Looking at an index value usually costs nothing. Using one is a different transaction, and the providers say so in the documents themselves:

• The CoinDesk 20 methodology ends: "Any commercial use of CoinDesk Indices Content requires a license." Content is defined to include the names of its indexes and rates.
• MarketVector's index guides: "The use of MarketVector™ Indexes in connection with any financial products or for benchmarking purposes requires a license."

What the licence costs is not published by any of the providers here. The nearest thing to a price is in fund filings, which have to describe the agreement even when they do not quote the number. Grayscale's 10-K for its Ethereum Classic Trust, filed on 12 March 2026, says the sponsor pays CoinDesk Indices "a monthly fee and a fee based on the NAV of the Trust" for its licence to the single-asset index that prices the trust — a fixed part and a part that grows with assets. The agreement dates from 1 February 2022, has been extended to 29 February 2028, and renews annually after that unless either side gives notice.

The same filing states the clause that matters most to anyone building on an index: under the licence, the index provider "may adjust the calculation methodology for the Index Price without notice to, or consent of, the Trust or its shareholders", and is under no obligation to consider their interests when it does. A licence buys the right to use the number. It does not buy a say in how the number is made.

The name is part of what is licensed, and fund names show it. The fund Hashdex lists on Nasdaq under the ticker NCIQ, which its own filing says tracks the NCI, took the index's new name with it: its March 2026 prospectus supplement is filed as the Hashdex Nasdaq CME Crypto Index ETF, two months after Nasdaq's rename.

There is also a cost upstream of the provider, which is not yours to pay but shapes what exists. An index is computed from exchange trades, and exchanges' terms can restrict exactly this use — the bitcoin page quotes Coinbase's clause against building "indexes, fixings, or other benchmarks" from its data without consent, and what exchange API terms actually let you do covers the rest of the chain. An index provider has to settle that question with every venue it reads. If you build your own basket from raw exchange data, so do you.

What you can do about it

Work out which of three things you are doing. The licence question turns on it, and so does almost everything else.

1. Looking at an index. Reading a published value on the provider's site, or quoting it in research with attribution, is what the public values are there for. Nothing on this page stops you.
2. Displaying or redistributing it. Putting live index values into an app, a dashboard you sell or an API response is data licensing — the same question as for any market data, asked of the index provider or of a vendor licensed to redistribute its values. Ask the vendor in writing whether their licence covers display to your users, and whether it covers derived data.
3. Building a product on it. A fund, a structured note, a token, a vault or a contract that settles against an index, or anything that uses the index's name in its own, needs a licence from the owner. The one such agreement described in a public filing above is a fixed monthly fee plus a fee on assets — not a subscription — and none of these providers publishes a rate card.

If you only need "the market" as a line on a chart, build your own basket and give it your own name. The five decisions above are not hard to reproduce; what you cannot reproduce is the trademark. A basket labelled "top 20 by market cap, capped at 25%, rebalanced monthly" says more than a borrowed index name, costs nothing to name, and can be changed when you like. Check the terms of whatever prices you feed it first — that is where the restriction actually bites.

Before comparing two index products, read five lines of each rulebook. The per-asset cap. The exclusion list — stablecoins, memecoins, privacy tokens, staked and wrapped assets. The custody and exchange requirements. The review frequency. And the price source, including the date it last changed. Two indexes that differ on the first line will diverge whenever bitcoin moves against the rest of the market, and neither is wrong.

Put the calendar in your system, not in your head. Reconstitution and rebalance dates are published in advance and constituents are announced days or weeks ahead. If anything you run — a dashboard, a reconciliation, a risk report — shows index constituents or weights, it should expect them to change on those dates and should expect weights to drift between them.

Pin the methodology version. When you cite an index, store the methodology version or date alongside the value, the way the documents here do: CD20 methodology of 7 July 2026, MVDA guide version 1.03. A value without the rulebook version it was computed under cannot be checked later, and every rulebook cited on this page was revised between December 2025 and August 2026.

If you are choosing a data vendor for index values, ask four questions. Is the vendor the owner, the administrator, the calculation agent, or a redistributor? Does its licence let you show the values to your own users? Are settlement values included, or only real-time? And will it tell you when the methodology changes, or will you find out from the change log? CoinDesk Data, Coin Metrics and Kaiko each sell index or reference-rate data alongside their market data; put all four questions to each of them before comparing prices.