Implied probability: turn a price into a break-even rate
Implied probability translates odds into a percentage. It shows the win rate required by a price under stated assumptions; it does not prove how likely an outcome really is.
Start with decimal odds
For decimal odds d, implied probability is 1 ÷ d. Multiply by 100 to express it as a percentage. Decimal 2.50 therefore implies 40%; decimal 2.00 implies 50%. This break-even interpretation assumes a win-or-loss cash bet with no fees.
American +150 converts to 2.50. American −110 converts to 1 + 100 ÷ 110, or about 1.9091. The second price requires approximately 52.38% wins among decided bets to break even.
Why both sides can add to more than 100%
| Outcome | Price | Implied probability |
|---|---|---|
| Side A | −110 | 52.38% |
| Side B | −110 | 52.38% |
| Combined | Both outcomes | 104.76% |
The sum exceeds 100% by roughly 4.76 percentage points. This is the quoted overround for this complete two-outcome set. It is not a measured statement of the operator’s realized profit, which depends on stakes, results and other factors.
Removing margin requires an assumption
A simple proportional normalization divides each implied probability by the total. In this symmetric example, 52.38 ÷ 104.76 gives 50% for each side. Normalized probabilities add to 100%, but that arithmetic does not prove that the game is truly a 50/50 event.
With asymmetric prices, proportional normalization assumes the margin scales proportionally across outcomes. Other margin-removal methods can give different answers. Use a complete set of mutually exclusive outcomes with matching settlement rules and a consistent time snapshot.
Do not confuse a price threshold with a prediction
Suppose your justified estimate is 50% while the price requires 52.38%. Those inputs imply negative expected value. Simply relabeling the market’s implied percentage as your own forecast adds no independent evidence.
A probability estimate needs a method, relevant inputs and a way to evaluate calibration. A recent hit rate on a small or selectively reported set of picks is not automatically a calibrated probability for the next event.
Check for outcomes the formula leaves out
A three-way market needs all three outcomes to assess its overround. Two moneylines sampled from such a market are incomplete. Push-capable markets require separate push treatment for an unconditional EV calculation; the simple price threshold applies to decided bets.
Try the numbers yourself.
Open the calculator with this guide’s example inputs. Change one assumption at a time and see what changes.
Open implied probability calculatorCommon questions
Is a normalized probability a verified fair price?
No. It is the result of a chosen margin-removal method applied to quoted prices. Market errors and model assumptions can remain.
Can I combine opposite prices from different times?
The arithmetic will run, but the total will not describe one coherent market snapshot. Record timestamps and matching rules.
Sources and example scope
The cited source defines implied probability and overround. The −110 example and discussion of normalization assumptions are original worked analysis.