How the market index works

Steam sales, because Steam's history shows what items sold for, not what sellers ask. Each day's price is what an item sold for on Steam that day, on average.

An index uses each item's median price over its last 7 days. For an item that sells on most days, one unusual day barely moves it. A lasting change shows up within a few days.

Steam's sales figures are final about two weeks after the day. Until then a day can still be missing or corrected. So the newest five weeks of an index, including which items are in it, can still shift. Older values only change when a rule on this page changes or older price data is corrected, and this page lists it when that happens.

A new item qualifies when, in the month before, it:

• sold on Steam on at least 20 days,
• sold for $1 or more on a typical day,
• sold at least once in the month's last three days,

and it first sold on Steam at least 18 months before. In our Steam data the typical new skin kept falling against older skins for more than a year after release. The 18 months are our choice based on that: an index follows established items, not that fall again with every new release.

That keeps out items that hardly trade, and very cheap items, where a one-cent step is already a move of more than 1%. An item already in the index stays with less: at least 10 days with a sale and one in the month's last week. That way a slower month does not swap items in and out. A skin enters once, not once per wear: in the version that traded the most money on Steam over the 12 months before (for example its Field-Tested StatTrak version). It stays in that version for as long as that version keeps selling.

Doppler and Gamma Doppler knives are left out: Steam sells every phase under one name, so their daily price depends on which phases happened to sell, not on the market.

Every item counts equally. The SkinGrind 100 picks its hundred items by how much money each traded on Steam over the last 12 months (each day's price times its number of sales), but once in, each counts the same as any other. An item already in keeps its place while it is still among the 150 most traded, so the hundred do not change with every busy month and are not always the top hundred. That cut-off of 150 is our choice. A different one would have given the SkinGrind 100 a clearly different level. Counting items by money traded would tilt an index toward whatever sold most recently, often new releases and items that had just spiked.

The index follows the average price change of its items, taken as a geometric average: an item that doubles and one that halves cancel out. Someone holding equal amounts of both would be 25% up, so an index is not the return of a basket. We use the geometric average because a plain average of noisy price changes climbs on its own over the years.

At the end of every month the items and their shares are set again by the rules above. The index carries on from the same level, so changing its items never makes it jump. Earlier parts of a chart follow the same rules, applied to the Steam sales of the time.

An item without a sale keeps the price of its most recent sales for up to a week. After seven days without a sale it leaves the index until a later month, and the others take over its share. It leaves at that last price, so the index does not show what selling it would have cost.

An index never stops. An item only leaves during the month while at least 5 others remain; otherwise it stays at its last price until the monthly update. If fewer than 5 items qualify at an update, the index carries on with the ones it has, and its page says so: with so few items a single item can move it a lot. If none qualify, the level stays where it was until one does.

The SkinGrind 100 holds 100 of the most traded skins, stickers and containers (cases, capsules and souvenir packages) that have sold on Steam for at least 18 months. It started once there were 100 to choose from, and it can briefly hold fewer when an item stops selling during a month. The Knives, Gloves, Rifles and Pistols indices hold every skin of that type that qualifies, the Cases index weapon cases, and the Stickers index stickers. Every collection has its own index from the first month with at least 5 items that pass the rules above.

Expensive knives and gloves trade mostly outside Steam, so many of them are missing here or priced from few sales. An index only holds items that sell often, so it says little about items that are hard to sell. Its items change every month, so over years its change can differ a lot from a fixed set of skins bought once and held. In the past, the way items join and leave has lowered what an index measured. How much, and in which direction, can vary. An index shows where prices went, not where they will go.

Rules as of October 3, 2026. If a rule changes or older price data is corrected, the date and the change are listed here.

All market indices