What is house edge?
House edge is the percentage of what you pay that the operator keeps, on average, over many plays. If a case costs $10 and the average value of what comes out is $8.50, the house edge is 15%. The operator keeps $1.50 of every $10, averaged across everyone who opens that case.
Nobody experiences the average. One person gets $200, twenty people get $2. But the operator does experience the average, because it sells thousands of cases, and that is why the operator always ends up ahead. The house edge is not a trick or a flaw. It is the business model of every case opening site and of Valve's own cases.
This guide is for anyone who wants to understand the maths before spending money on cases. We do not recommend opening cases as a way to get skins or make money. If you do open them, the responsible gaming page has practical limits, and the case opening hub explains how we assess sites.
How do you calculate the house edge of a case?
You need two things: the probability of each outcome, and what each outcome is worth to you. Then:
- Multiply each item's probability by its value.
- Add all of those up. That is the expected return per case.
- Divide by the case price. That is the RTP, the return to player.
- House edge = 100% minus RTP.
A made-up example with a $10 case and four possible items:
| Item | Probability | Market value | Probability × value |
|---|---|---|---|
| A | 80% | $2 | $1.60 |
| B | 15% | $8 | $1.20 |
| C | 4.5% | $60 | $2.70 |
| D | 0.5% | $500 | $2.50 |
| Total | 100% | $8.00 |
Expected return $8.00 on a $10 case. RTP 80%. House edge 20%.
The house edge calculator does this for any table you enter. Two details matter a lot when you use it:
- Use the value you can actually get. If you will sell the item on the Steam Market, Valve takes 5% plus 10% per its Community Market FAQ, and the money stays in your Steam Wallet. If you will sell on a marketplace, use its after-fee price. A site's own displayed "value" is usually the most generous number available.
- Use current prices. A case's edge changes every time the prices of its contents move.
Notice in the example that item D, at half a percent, contributes as much to the average as item C. That is normal. In almost every case, most of the expected value sits in the rare outcomes, which most people never see.
What are the odds of a Valve case?
Valve's weapon cases all use the same odds per rarity tier. Valve disclosed them in 2017 to meet Chinese regulations on loot boxes, through its publishing partner there, and community tracking of very large samples of openings since has matched them.
| Tier | Chance per case | About 1 in |
|---|---|---|
| Mil-Spec (blue) | 79.92% | 1.25 |
| Restricted (purple) | 15.98% | 6.3 |
| Classified (pink) | 3.20% | 31 |
| Covert (red) | 0.64% | 156 |
| Rare special item (knife or gloves, gold) | 0.26% | 385 |
Within a tier, each skin is equally likely. So if a case has five Mil-Spec skins, each is about 16% per opening. StatTrak versions appear at about one in ten within a tier.
The drop rates tool shows these odds, and the case odds calculator turns them into questions like "how many cases for a 50% chance at a knife" (the answer is in the hundreds, and it never reaches certainty).
Since 22 October 2025, five Covert skins can also be traded up into a knife or gloves per Valve's release notes. That gives knives a second source and changed their prices, but it does not change case odds.
What is the expected value of opening a Valve case?
You calculate it exactly like the example above, using the odds table and the current Steam Market prices of every skin in the case, at the wear distribution cases produce. Community calculations for popular cases regularly land far below the combined cost of the case and key, with most of the value coming from the Covert and knife slots.
The intuition is simple. About 96% of openings produce a Mil-Spec or Restricted skin. Most of those are worth a small fraction of the key price alone. The rare tiers carry the average, and the average is still below what you paid.
Two things make Valve cases worse than the raw RTP suggests:
- Fees on the way out. Selling the skin on the Steam Market loses about 13% of the buyer price to fees, and the proceeds cannot be withdrawn. Selling elsewhere has its own fees.
- Wear. Cases produce a spread of floats. The prices you see for Factory New copies do not apply to the Field-Tested you are likely to get.
The case simulator lets you open thousands of simulated cases with real odds and see what a long run looks like without spending anything. It is the cheapest way to feel the house edge.
How do third-party case sites set their edge?
Third-party case opening sites do not use Valve's cases. They build their own item tables: a list of skins, a probability for each, and a case price. They can set the numbers however they want, and they can change them.
Most sites advertise a higher return than Valve's cases, and it is often true. A site that sets a 90% RTP has a 10% house edge, better than Valve's cases by most calculations. But three things shift the picture:
- The site prices the items. If it values a skin at $100 that sells for $80, the real RTP is lower than the displayed one.
- Withdrawal has conditions. Converting site balance to a skin in your Steam inventory may involve minimums, availability, or a wait.
- The edge compounds across features. Upgraders, battles and other modes have their own edges on top of the case edge.
Provably fair systems, explained in how provably fair works, let you check that each roll matched the table. They do not check the table against your interests. A site can be fully verifiable and still take 20% on every case. Only the calculation tells you.
We do not state any site's house edge, fees or policies in guides. Our case opening hub lists sites we have looked at with dated notes, and each site's own odds page plus the house edge calculator gives you the number for any case.
Why does a low house edge still lose over time?
Because the edge applies to every play, and plays add up.
Suppose a site has a 5% house edge and you open $20 of cases a day. On average you lose $1 a day. That is small. But you do not stop; you reinvest what you win. Over a month of daily play, your $20 has been through the machine many times, and each pass takes 5%. The expected loss is not 5% of $20. It is 5% of everything you ever put through, and the total put through is far larger than the money you started with.
Variance hides this. Some weeks you are up. The up weeks feel like skill or luck turning. They are noise around a slope that only points one way. Casinos are built on exactly this, and case sites are the same maths with skins instead of chips.
The lower the edge, the longer the slope takes to show. It still shows. The only sure way to beat a positive house edge is not to play, and the only way to limit it is to decide in advance how much you will put through and stop there. The responsible gaming page covers how to set that limit and where to get help if stopping has become hard.
How do you check a site's real edge yourself?
Ten minutes, and it tells you more than any review.
- Find the odds table for a case. It should list every item and its probability. If it does not exist, stop; you cannot evaluate what you cannot see.
- Check that the probabilities add to 100%.
- Price each item at what you could sell it for. Use the Steam Market after fees, or a marketplace after fees, not the site's own figure.
- Enter the table in the house edge calculator.
- Compare the result with the site's claimed RTP, if it publishes one. A big gap means the site's item prices are inflated.
- Repeat for two or three cases, including a cheap one and an expensive one. Edges often differ by case.
- Verify a few rolls with the provably fair verifier if the site offers it, so you know the table is actually used.
Then you know the price of playing. Whether to pay it is a separate decision.
When is opening a case a reasonable choice?
Rarely, and only with clear eyes. Opening a case is paying for entertainment with a small chance of a valuable item attached. That can be a fine thing to spend money on, the same way a movie ticket is, if:
- You know the expected loss before you start and are fine with it.
- The amount is one you would spend on any other entertainment without a second thought.
- You are not trying to win back a previous loss.
- You would not be upset to receive the most common outcome.
- You are of legal age where you are, and the site is allowed where you are.
It is not a reasonable choice as a way to acquire a specific skin. Buying the skin costs less than the expected cost of opening for it, every time, for every skin. It is not a way to make money. And it is not a reasonable choice for anyone who has noticed that they keep going past the limit they set.
Case battles, covered in case battles explained, add a winner-takes-all layer that increases variance without changing the edge. The same maths and the same limits apply.
The house edge is the one number in case opening that does not depend on luck. Learn to calculate it, and you will always know exactly what a case really costs.