What is a crypto index?

A crypto index is a number that tracks the value of a defined group of crypto assets over time. Instead of following one coin, it follows a basket: which assets are in it, how much of each it holds, and how both change are all set by published rules. When people ask how "the crypto market" did this week, a well-built index is one of the clearest ways to answer.

This page explains what goes into a crypto market index, why the rules matter more than the starting list of coins, and how to read the figures an index publishes. It uses the C100, a rules-based index of the 100 largest eligible crypto assets, as a running example; its numbers below update from the index data.

The idea behind any index

Stock market indexes have existed for well over a century. The principle is the same in crypto: pick a universe, choose the members with rules, give each a weight, and calculate one number from their prices.

Three questions define every index:

1. Which assets are included? A universe and a set of eligibility rules decide this. A broad index might hold the 100 largest assets; a narrow one might hold only a sector, such as decentralized finance.
2. How much of each? This is the weighting. The most common choice is market-capitalization weighting, where larger assets get larger weights. Others include equal weighting and capped weighting.
3. When does it change? Prices move every second, but membership and target weights are usually reset on a schedule, at reviews called rebalances and reconstitutions.

An index is not a fund and holds nothing. It is a calculation, published so that anyone can compare performance against a defined benchmark.

How a crypto index chooses its assets

The crypto market lists thousands of tokens, and a ranking by market capitalization on a price site is not a usable index on its own. Several kinds of token behave nothing like the rest of the market, and many listed tokens are hard to trade.

A careful crypto index therefore starts with exclusions and screens. The C100, for example:

• Removes tokens that track something else. Stablecoins follow a currency, wrapped and bridged tokens follow another coin, liquid-staking receipts follow a staked asset, and tokenized gold or stocks follow off-chain assets. Including them would double count or add non-crypto exposure.
• Takes the top 150 of what remains, ranked by market capitalization on each selection date.
• Requires a track record: at least 90 days of price history.
• Requires liquidity: a 30-day median daily trading volume of at least $5 million, and trading on at least 10 market pairs.

Only after these rules does the index select its members. The current C100 holds 100 constituents; the largest are shown below.

How a crypto index weights its assets

Weighting decides how much each asset moves the index. Pure market-cap weighting mirrors the market: at the latest C100 review, Bitcoin was 68% of the combined market value of the constituents, so a pure market-cap index would give it that weight. That is simple, but in crypto it means one asset can dominate the result.

Most broad indexes therefore cap weights. The C100 limits Bitcoin and Ethereum to 20% each and every other asset to 10%, and the assets above 4.5% may not total more than 48%. Weight removed by a cap is shared among the remaining assets in proportion to their size. On the latest review, Bitcoin's weight was 14.2% and Ethereum's 14.6%, and the ten largest constituents together made up 68%.

An equal-weight index takes the opposite approach and gives every member the same weight. Our page on equal weight vs market cap compares the two on the same assets.

Rebalancing and reconstitution

Between reviews, weights drift as prices move: an asset that doubles takes a larger share. At each review the index resets to its rules.

• A rebalance resets weights to their targets without changing membership. The C100 rebalances on the first Monday of every month.
• A reconstitution also reviews membership: assets that no longer qualify leave, new ones join. The C100 does this quarterly, in January, April, July and October.

To limit turnover, many indexes use a buffer. In the C100 an existing member stays while it ranks in the top 120 eligible assets, and a newcomer must rank in the top 90 to join. The next C100 review is a rebalance on December 7, 2026.

The detailed mechanics, including a worked example from the latest real review, are on how crypto index rebalancing works.

How the index level is calculated

The published number, the index level, starts at a base value on a base date. The C100 started at 1,000 on January 6, 2020. From then on:

level = sum of (units × price) ÷ divisor

Each asset holds a number of units set at the last review. The divisor is a scaling number that is adjusted at every review so that the level just after the review equals the level just before it. Changing the constituents or their weights therefore never makes the index jump; only price moves do.

The C100 is at 7,761.88. Because the units, prices and divisor behind every daily close are published, anyone can recompute the level themselves.

Point-in-time data and survivorship bias

An index's history is only as good as its data. A common mistake is to build a "backtest" from today's list of coins. That quietly removes every project that collapsed, was delisted or faded, and makes past results look better than they were. This is called survivorship bias.

A point-in-time index uses only the information available on each historical date. The C100's history before its live launch on November 1, 2026 is a backtest built that way: each review used the market ranking of that day, including assets that later failed. Terra's LUNA, for instance, was a large constituent in early 2022 and its collapse is part of the record.

How to read crypto index figures

When an index publishes performance, a few numbers do most of the work:

• Total return: the change in level over a period. The C100 has returned +685% since its base date.
• Annual return (CAGR): the yearly rate that would produce the total return. For the C100 it is +35.2% a year since January 6, 2020.
• Volatility: how widely daily returns swing, annualized. The C100's is 72%.
• Maximum drawdown: the largest fall from a peak to a later low. For the C100 it is −80%.

These figures describe the past and are not a forecast. They become most useful when compared with something else, such as holding Bitcoin alone.

Different kinds of crypto index

Indexes differ in what they try to capture. The C100 publishes a small family on the same data and rules:

A narrow index such as the C25 concentrates on the largest assets. An equal-weight index gives small assets the same say as large ones. An ex-Bitcoin index shows how the rest of the market moved without its largest asset.

Frequently asked questions

What is a crypto index in simple terms?

It is a single number that tracks a defined basket of crypto assets, chosen and weighted by published rules, so the performance of that part of the market can be followed and compared over time.

Is a crypto index the same as the top 100 coins on a price site?

No. A price-site ranking includes stablecoins, wrapped tokens and thinly traded assets, and changes every minute. An index applies exclusions, liquidity screens and a review schedule, so its members and weights are stable and reproducible. The top 100 crypto index page explains the differences.

How often does a crypto index change?

Prices change it continuously. Its rules change it only at reviews. The C100 resets weights monthly and reviews membership quarterly, and it applies token migrations and emergency removals when they happen.

Can I invest in the C100?

No. The C100 is an informational index, not an investable product, and nothing here is investment advice.

Where do the numbers come from?

The C100 uses daily market data from CoinMarketCap and its published methodology. Every rule and every discretionary decision is documented in the governance pages.