BO1 / BO3 / BO5 Series Win Probability Calculator
A per-map edge compounds over a series. Enter a map win probability and this returns the BO1, BO3 or BO5 series probability, the fair series price, and the full correct-score split — or set each map separately to price a veto.
- Series win
- 64.80%
- Series loss
- 35.20%
- Fair series price
- 1.54
| Correct score | Probability |
|---|---|
| 2–0 | 36.00% |
| 2–1 | 28.80% |
| 1–2 | 19.20% |
| 0–2 | 16.00% |
Enter a series price to see the per-map win rate it corresponds to.
Assumes each map is independent and equally likely to go your way. Real series aren’t quite like that: the veto steers a series onto maps each side picked, so “set each map separately” is the more honest mode when you have a view on the map pool. This is arithmetic on your own numbers, not a forecast.
Informational and educational only. 18+. This tool performs arithmetic on figures you enter; it does not recommend any outcome and makes no prediction.
The same edge, three formats
Read down a row and you get the single most useful fact about series formats: a small per-map edge is nearly invisible over one map and substantial over five. Every figure is computed by the code the calculator runs.
| Win % on a map | BO1 series | BO3 series | BO5 series |
|---|---|---|---|
| 50% | 50.0% | 50.0% | 50.0% |
| 55% | 55.0% | 57.5% | 59.3% |
| 60% | 60.0% | 64.8% | 68.3% |
| 65% | 65.0% | 71.8% | 76.5% |
| 70% | 70.0% | 78.4% | 83.7% |
| 80% | 80.0% | 89.6% | 94.2% |
This is why format matters so much in Counter-Strike. Group stages built on BO1s produce upsets that the same teams would rarely produce in a BO3, and a BO5 final is the most favourite-friendly format the game plays. None of that is a claim about any particular team — it is what the arithmetic does to any edge you put into it.
The one thing it cannot see is the veto, which deliberately steers a series onto maps each side chose. That is what the per-map mode is for; our study of what teams actually ban is a reasonable starting point for the numbers to put in it.
Series and format questions
- How do you work out a BO3 win probability from a map win probability?
- A team winning each map with probability p wins a BO3 with probability p²(3 − 2p): it can win 2–0, or drop either of the first two maps and win the decider. At p = 60% that comes to 64.8%. For a BO5 it is p³(10 − 15p + 6p²), or 68.3% at the same per-map rate.
- Why does a BO3 favour the better team more than a BO1?
- Because more maps mean less variance. A single map is close to a coin flip even between mismatched teams; over three or five, the better side has more chances for its edge to show. A 60% map team wins 60% of BO1s but 64.8% of BO3s and 68.3% of BO5s — the same edge, compounded.
- Does this account for the map veto?
- Only if you tell it to. The simple mode assumes the same win probability on every map, which the veto makes untrue — each side picks maps it is better on. "Set each map separately" is the honest mode when you have a view on the map pool: give each map in the series its own probability and the maths handles the rest.
- What are the assumptions?
- Each map is treated as independent, and in simple mode as equally likely to go your way. Real series may not be independent — momentum, and reading an opponent between maps, are both plausible. This is arithmetic on the numbers you supply, not a forecast, and it should be read that way.
- What is a fair series price?
- One divided by the series win probability, with no margin in it. A real quoted price will always be shorter than that, because the margin sits on top — you can measure that gap with the vig calculator, or remove it with the no-vig calculator.
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