How crypto index rebalancing works

An index is defined by its rules, but prices ignore rules. Between reviews, every asset's weight drifts as its price moves, and the market ranking shifts underneath the index. Rebalancing is how an index returns to its rules. This page explains the mechanics step by step, from target weights and caps to the divisor that keeps the index level from jumping, and walks through the latest real C100 review.

Drift: why rebalancing is needed

At each review, the C100 sets a target weight for every constituent and converts it into a number of units. From then on the units stay fixed and the weights move with prices. If one asset doubles while the rest of the index is flat, its weight roughly doubles too.

Left alone, drift undoes the design. A capped asset can climb well above its cap, and an asset that has fallen far can shrink to almost nothing. Rebalancing resets the weights to the rules on a fixed calendar.

Rebalance vs reconstitution

The C100 has two kinds of scheduled review, both effective at 00:00 UTC.

• A rebalance, on the first Monday of every month, resets weights to their targets. Membership does not change.
• A reconstitution, on the first Monday of January, April, July and October, first reviews membership and then resets weights.

Both use data from the day before the review, the 00:00 UTC values of the previous date, and prices at the review's own 00:00 UTC close. The next review is a rebalance on December 7, 2026.

Step 1: who is in (reconstitutions only)

At a reconstitution the index rebuilds its eligible list from scratch: it removes excluded token types, takes the top 150 by CoinMarketCap's ranking, and keeps only assets with at least 90 days of history, a 30-day median volume of at least $5 million and at least 10 market pairs.

It then applies the buffer rule:

• an existing constituent stays while it ranks in the top 120 eligible assets;
• a new asset joins only if it ranks in the top 90;
• remaining places go to the highest-ranked eligible assets, and if too many qualify, the lowest-ranked are dropped.

The buffer exists because rankings near the boundary are noisy. Without it, an asset ranked 100th one quarter and 101st the next would leave and rejoin repeatedly, creating turnover with no meaning. Every addition and removal is published with its reason; you can see them on each asset's page and in the monthly reports.

Step 2: target weights and caps

Next, the index computes target weights from market capitalization and applies its caps in order:

1. Raw weights. Each constituent's market cap divided by the total.
2. Single-asset caps. Bitcoin and Ethereum are limited to 20% and every other asset to 10%. Weight above a cap is redistributed to the uncapped assets in proportion to their weights, repeating until nothing exceeds its cap.
3. Aggregate cap. The assets weighing more than 4.5% may not together exceed 48%. If they do, they are scaled down to 48%, and the freed weight is redistributed to the other assets, none of which may rise above the threshold. An asset that the scaling would take below the threshold leaves the scaled group, so a smaller asset can never end up outweighing a larger one.

From the December 7, 2026 rebalance, the assets outside the scaled group are held at 4.4% rather than exactly at the threshold, so that no asset sits on the boundary.

At the latest review, 8 assets had their target weight set by a cap rule rather than by market cap alone.

Step 3: units and the divisor

Target weights are turned into units: each asset gets the number of units that makes its value equal its target share of the index. Then the divisor is reset.

The index level is always the sum of units × price, divided by the divisor. Changing the units changes that sum, so the divisor is recalculated to keep the level just after the review exactly equal to the level just before it. A review therefore never moves the index by itself; only price changes do.

The C100 does this arithmetic in 40-digit decimals, and the units, divisor and prices behind every daily close are published so the level can be recomputed independently.

A worked example: the latest C100 review

Here are the figures from the most recent C100 review, the rebalance on November 2, 2026:

Three things to notice:

• The level did not move. The divisor changed from its old value to its new one exactly so that the level stayed the same at the moment of the review.
• The largest changes are in the largest and the capped assets. Assets near a cap are trimmed back to it after a rally, or topped up after a fall.
• Turnover was 2.7%. One-way turnover adds up the increases in weight across all assets: the share of the index that had to be reallocated. Monthly rebalances usually have low turnover; reconstitutions, which change members, usually have more.

Events between reviews

Two kinds of event change the index between scheduled reviews:

• Token migrations. When a project replaces its token with a new one at a published ratio, the index converts its units at that ratio, as a holder would. The divisor keeps the level unchanged.
• Removals. An asset can be removed after a delisting, loss of peg or exploit, through a proposal and approval that are written to an audit log. Any asset with no price for more than 3 days is removed automatically at its last price.

All such decisions are listed in the governance decision log.

Why rebalancing affects returns

Rebalancing is not neutral for performance. Each month it sells part of whatever has risen above its target and buys more of whatever has fallen below it. In a market that trends strongly in one asset, this tends to lag; in a market where leadership rotates, it can help. The result depends on the period. You can see how the C100's rules have played out against Bitcoin on crypto index vs Bitcoin, and against an equal-weight version on equal weight vs market cap.

Frequently asked questions

How often is the C100 rebalanced?

Weights are reset on the first Monday of every month at 00:00 UTC. Membership is reviewed quarterly, on the first Monday of January, April, July and October.

Why doesn't the index level jump at a rebalance?

Because the divisor is recalculated at every review so that the level after the change equals the level before it. Only price moves change the level.

What is the buffer rule?

A rule that reduces turnover at the boundary: existing constituents stay while they rank in the top 120 eligible assets, and new assets must rank in the top 90 to join.

What does it mean when an asset is capped?

Its target weight was set by a cap rule instead of by its market cap alone, because its market cap would otherwise give it more than the cap allows. At the latest review, 8 assets were capped.

Can I see the weights before and after each review?

Yes. The rebalances page lists every review since 2020, each monthly report shows the largest weight changes, and every asset page has its full weight history.