Odds Calculator
Convert between odds and probability — odds for/against to probability, or probability to odds in favor.
How it works
- 1In Odds → Probability mode, enter favorable outcomes (odds for) and unfavorable outcomes (odds against). Probability = odds-for ÷ (odds-for + odds-against).
- 2In Probability → Odds mode, enter a probability as a percentage (0–99.99%). The odds in favor equal p ÷ (1 − p), shown as an “x : 1” ratio.
- 3All conversions use exact arithmetic with no rounding until display, so results are as precise as the inputs allow.
Use cases
- Evaluate betting lines by converting quoted odds to an implied win probability before placing a wager.
- Check whether a project’s estimated success rate (e.g. 75%) matches the 3 : 1 odds a stakeholder quoted.
- Teach introductory probability by showing the direct relationship between ratio-based odds and decimal probabilities.
Frequently asked questions
What is the difference between odds and probability?
Probability is favorable outcomes divided by all outcomes (0–1). Odds compare favorable to unfavorable outcomes — e.g. 3 : 1 odds mean 3 wins per 1 loss, a probability of 3 ÷ 4 = 0.75.
Why does Probability → Odds not accept 100%?
Odds in favor = p ÷ (1 − p). When p = 1 the denominator is zero, making the odds infinite — a certainty has no meaningful odds ratio.
Are these the same as fractional (UK) betting odds?
Yes. Fractional odds like 3/1 represent the same 3 : 1 ratio. Enter 3 for odds-for and 1 for odds-against to get the implied probability of 0.75 (75%).
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