Convert American, decimal or fractional betting odds to implied probability, the break-even win rate, or turn a probability back into fair odds.
Implied Probability Formula and Method
Decimal odds = total return / stake
Decimal odds describe total returned per unit staked. Fractional odds describe profit relative to stake. Positive American odds describe profit on a 100-unit stake; negative American odds describe the stake needed for 100 units of profit. Converting formats keeps the underlying offered price unchanged.
How to Use This Calculator
Choose the odds format or reverse probability mode, enter the shown input, then select Calculate. Fractional input uses profit/stake such as5/2; American odds must be≥+100 or≤−100. Reverse mode accepts0.0001% to99.9999% and reports corresponding zero-margin decimal odds. Expand Calculation details for formulas.
Worked Example
With the example inputs in the table, the result is 40%. These formats describe the same offered price.
Implied probability = 100 / decimal odds
Input and Example Guide
| Input or category | Example or weight | Entry guidance |
|---|---|---|
| Method | Convert an offered price | Choose the odds format used by your quoted price. |
| Input odds format | Decimal odds | Choose the odds format used by your quoted price. |
| Offered odds (selected format) | 2.5 | Use the stated unit; retain available precision. |
Interpreting the Result
The reciprocal of decimal odds is the cash-stake break-even probability. It is an implied price probability, not an independent estimate of an outcome’s chance. Entering a probability in the reverse method gives its corresponding zero-margin price. Rounded display prices may differ slightly when converted back.
Implied probability includes the market margin; it is not a measured chance of winning.
Assumptions and Common Input Errors
Conversions assume the same cash-stake settlement conditions and exclude commission or other charges. Equivalent decimal odds must exceed1 and be at most1,000,000. Converted display odds are rounded; no currency amounts or payouts are calculated.
Saving and Revising a Scenario
A successful calculation is saved in this browser and can be restored on the next visit. Editing an input retains the previous result with an Inputs changed warning until Calculate is selected. Reset clears this calculator’s fields and saved state; user inputs begin empty.
American odds to implied probability: for positive odds A, p = 100/(A + 100); for negative odds A, p = |A|/(|A| + 100). Multiply p by 100 for a percentage. For example, −250 gives 250/(250 + 100) ≈ 71.429%.
Sources
Smarkets: implied probability formulas for decimal, fractional and American odds. This calculator converts prices; it does not estimate a true win probability or remove market margin.
