What is CS2 coinflip?
CS2 coinflip is the simplest gambling game on skin sites. Two sides, one result. You put up a stake, the coin lands on one side, and one side takes the pot. The sides are usually shown as the CT and T logos from the game, or as two coloured coins.
Because it looks like a fair coin, people treat coinflip as the "honest" game on these sites. That is half right. On a provably fair site the coin really does land on each side half the time. The catch is in what you get paid when you win, and this page is mostly about that.
How does a coinflip round work?
There are two designs, and it helps to know which one you are looking at.
Player versus player. One player creates a lobby, puts in skins or balance, and picks a side. Another player joins with a stake of about the same value and gets the other side. The site flips the coin, takes a cut from the pot, and gives the rest to the winner. Lobbies are listed on a page where you can see the stake and the side already taken.
House banked. You bet against the site directly. You pick a side and a stake, the site flips at once, and a win pays a fixed multiplier. The multiplier is usually just under 2x, or it is exactly 2x and the site takes a fee on the way in or out. Either way the site is your opponent.
Both designs use the same coin. They differ in how the site gets paid, and that is where the edge lives.
What is the house edge in coinflip?
The house edge is the share of every stake the site keeps on average. In coinflip it is easy to compute because there are only two outcomes.
Start with the house-banked version and a 2x payout. Suppose the site keeps an edge h. It can do that by paying 2 x (1 - h) on a win instead of 2. Your expected return is:
Expected return = 0.5 x 2 x (1 - h) = 1 - h
Now here is the useful way to think about it. A 2x payout with an edge is the same, in money terms, as a fair 2x payout with a lower win chance. Set 2 x p = 1 - h and solve for p:
Equivalent win chance = (1 - h) / 2
At a 5% edge, that is 0.95 / 2 = 0.475, or 47.5%. The coin still lands your way 50% of the time, but you are paid as if it landed your way 47.5% of the time. That 2.5 point gap, doubled, is the 5% the site keeps.
Player versus player works out the same. Two players stake $10 each for a $20 pot. With a 5% rake the site keeps $1 and pays $19 to the winner. Your expected value is 0.5 x 19 - 10 = -0.5, which is 5% of your stake. Rake and house edge are two names for the same cost.
Sites set their own edge or rake and it is not always shown clearly. Our house edge calculator lets you plug in any number and see the long-run cost, and house edge explained covers the idea for every game type.
What does the edge cost over many flips?
The first table shows how the equivalent win chance moves with the edge. The 5% row is an example, not a claim about any specific site.
| House edge or rake (example) | Payout on a $10 win | Equivalent win chance | Average loss per $10 flip |
|---|---|---|---|
| 0% | $20.00 | 50.0% | $0.00 |
| 2% | $19.60 | 49.0% | $0.20 |
| 3% | $19.40 | 48.5% | $0.30 |
| 5% | $19.00 | 47.5% | $0.50 |
| 8% | $18.40 | 46.0% | $0.80 |
| 10% | $18.00 | 45.0% | $1.00 |
Fifty cents a flip sounds small. Coinflip lobbies fill in seconds, so 100 flips in an evening is easy. At a 5% edge and $10 a flip, that is $50 of expected loss, and the swings around that average are large. Some nights you will be up $100 and some nights down $200, but the centre of the range moves down by $0.50 every flip.
The second table matters for the myths section below. It shows how often a losing streak happens on a fair coin.
| Losses in a row | Chance it happens on any given start | Martingale stake on the next flip (from $10) |
|---|---|---|
| 3 | 12.5% | $80 |
| 5 | 3.1% | $320 |
| 7 | 0.8% | $1,280 |
| 10 | 0.1% | $10,240 |
How does provably fair work for coinflip?
Provably fair lets you check that the flip was decided by fixed values the site could not change after seeing the stakes. For coinflip the setup is close to cases and roulette.
The site holds a secret server seed and shows you its hash before the flip. You supply, or the site assigns, a client seed. A nonce counts up by one for each flip so the same seeds never produce the same result twice. The site combines the server seed, client seed and nonce with a hashing function, usually HMAC-SHA256, and gets a long hex string.
Turning that string into a side is simple. Take the first several hex characters, convert them to a number, and scale it to a value from 0 to 1, or from 0 to 99.99. If the value is below the halfway mark, one side wins. If it is at or above, the other side wins. Because hash output is spread evenly, each side gets exactly half the range.
Player-versus-player sites often add a public seed as well, such as the hash of a future blockchain block, so that neither player nor the site could know the result when the lobby was created. The block hash is only known once the block exists, which is after both stakes are in.
After the flip, the site reveals the server seed. Paste the seed, its hash, your client seed and the nonce into our provably fair verifier to confirm the hash matches and the roll lands on the side the site showed. For the full method and what it does not prove, read how provably fair works. It proves the flip was not rigged. It does not prove the rake is fair or that the site will pay out.
What are the common myths about coinflip?
Coinflip is where the gambler's fallacy feels most convincing, because a coin is something everyone thinks they understand.
"T has hit four times in a row, so CT is due." Each flip comes from its own hash with its own nonce. The coin has no memory. After four T results, the chance of a fifth is still 50%. Sites show streak history because people like to look at it, not because it means anything.
"Double after every loss and you cannot lose." This is martingale. Look at the second table. A run of 7 losses happens about once in every 128 starts, and by then you are staking $1,280 to win back $10. A run of 10 happens about once in a thousand starts and needs $10,240 on the table. Long sessions hit these runs. Site maximum bets and empty balances stop the system exactly when it needs to keep going, and every stake along the way still pays the edge.
"Coinflip has no house edge because it is player versus player." The rake is the house edge. The site is not risking anything on the flip, it is charging both players for the flip. The maths above shows the two designs cost the same at the same percentage.
"Big lobbies are safer because the site would not dare rig them." Provably fair, not stake size, is what makes a flip checkable. A big lobby on a site that does not publish hashes is just a big unverifiable flip.
"I can read the bots." Some sites fill lobbies with house bots. A bot opponent is still on the other side of a hash-decided coin. It has no pattern to read.
How do you set limits before you play coinflip?
Coinflip is dangerous for a specific reason. It feels like a fair, simple bet, so people stake more per round than they would on cases or crash, and the rounds take seconds.
Before you deposit, set three numbers. The most you will deposit this week, the loss at which you stop for the day, and a time limit for the session. If the site has deposit limits, loss limits or a cooldown in its settings, switch them on now. They are much easier to set before the first flip than after a losing run.
Pick a stake you can lose ten times in a row without it mattering, because the table above says you will see that streak eventually. Never raise your stake to recover a loss. Withdraw wins rather than rolling them back in, because every flip charges the edge again.
If you notice you are chasing, betting more than you planned, or hiding your play from people close to you, stop and use the site's self-exclusion tool. Our responsible gaming page lists free, independent help services.
Coinflip is often the entry point to the other games on these sites. Our roulette and crash hubs explain those with the same plain math.