🎲 How do CS2 case odds work?

Rarity tiers and official odds

Every item in a CS2 weapon case belongs to one of five tiers: Mil-Spec (blue), Restricted (purple), Classified (pink), Covert (red) and Rare Special Item (gold: knives and gloves). In 2017 Valve published the case odds because of regulations in China: Mil-Spec 79.92%, Restricted 15.98%, Classified 3.20%, Covert 0.64% and Rare Special Item 0.26%.

First a tier is chosen, then one of the items in that tier is picked with equal probability. So if a case has two Covert skins, each one has half of 0.64%, roughly 0.32%. The more items a tier contains, the harder it is to get one specific skin from it.

Odds on KasaSim

Because KasaSim is a simulator, it is deliberately a bit more generous: Mil-Spec 74%, Restricted 19%, Classified 5%, Covert 1.5% and Rare Special Item 0.5%. Rare items drop about twice as often as in the real game. If a case lacks some tiers (for example the Knife Case, which only contains knives), their share is spread proportionally over the tiers that exist. Every case page lists that case's exact odds.

🃏 Joker mode triples the case price but sharply raises the odds of rare items: Rare Special Item goes up to 2.5% and Covert to 4.5%. Joker is handy for chasing big wins on expensive cases, or for completing collections on cheap ones.

How many cases does a knife take?

At 0.26%, a knife or gloves drop about once every 385 cases on average; at KasaSim's 0.5% that falls to 200. But an “average” is not a guarantee. Someone who opens 200 cases still has about a 37% chance of seeing no knife at all, while a lucky player might find one in their very first case.

The gambler's fallacy

Every opening is independent: previous results don't affect the next one. Going 100 cases without a knife does not raise your chances on case 101. This is called the gambler's fallacy, and it is the most common mistake people make when opening cases. On KasaSim, too, every result is decided fresh on the server with the same odds.

Expected value: does a case really pay?

A case's expected value is the sum of every outcome's value multiplied by its probability. In real CS2, once the key price is included, opening cases loses money on average; the big wins come from a small number of lucky openings. On KasaSim, the “about” section on each case page shows that case's average return, the chance of a profit and the chance of doubling the price. Because the money here is fake, you can experience this maths without any risk.