What is the difference between probability and odds?

Probability is the ratio of favorable outcomes to total outcomes (e.g. 0.25 = 25%). Odds express the ratio of favorable outcomes to unfavorable outcomes (e.g. 1:3, or "1 in 3 chance against you"). They carry the same information but in different scales.

How do I convert probability to fractional odds?

Subtract the probability from 1 to get the "against" part, then divide: fractional odds = (1 − p) / p. For p = 0.25, that is 0.75 / 0.25 = 3/1. The tool simplifies the fraction automatically.

What are decimal odds?

Decimal odds represent the total payout per unit staked, including the stake itself. Decimal odds = 1 / probability. For a 25% chance, decimal odds = 1 / 0.25 = 4.00, meaning a $1 bet returns $4 total ($3 profit + $1 stake).

Can I enter fractional odds like 5/2?

Yes. Select "Fractional odds" as the input format and type 5/2 (or 5:2). The tool will parse the numerator and denominator and compute the equivalent probability and other formats.

What is the odds ratio (for / against)?

The odds ratio shows how many ways an event can happen vs. how many ways it cannot. A 25% probability means 1 way for every 3 ways against, written as 1:3. This is widely used in medical statistics and sports betting.

What happens at 0% or 100% probability?

These are edge cases: a 0% probability means the event is impossible (odds of 0:∞) and a 100% probability means the event is certain (odds of ∞:0). The tool shows a friendly message for these boundary inputs.

Probability To Odds Converter

Name: Probability To Odds Converter
Availability: InStock
Author: Nham Vu

Enter a probability or odds value and instantly convert between percentage, decimal, fractional, and for/against odds formats.

Input

Input Format

Probability (%)

Enter a value between 0 and 100.

Quick Examples

Enter a value on the left to see all conversions.

Common Probability — Odds Reference

Probability	Fractional	Decimal	For : Against
10%	9/1	10.00	1 : 9
20%	4/1	5.00	1 : 4
25%	3/1	4.00	1 : 3
33.3%	2/1	3.00	1 : 2
50%	1/1	2.00	1 : 1
66.7%	1/2	1.50	2 : 1
75%	1/3	1.33	3 : 1
80%	1/4	1.25	4 : 1
90%	1/9	1.11	9 : 1

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Summary

Enter a probability or odds value and instantly convert between percentage, decimal, fractional, and for/against odds formats.

How it works

Select your input format: probability (%), decimal probability, fractional odds, or decimal odds.
Type your value into the input field.
The tool computes all equivalent representations in real time.
Copy any output field with a single click.
Use the reference table at the bottom for common probability–odds pairings.

Use cases

Convert implied probability from bookmaker odds.
Check the odds ratio for a statistical experiment.
Translate fractional betting odds into a win probability.
Verify decimal odds before placing a wager.
Teach probability concepts using multiple equivalent representations.
Convert research data between probability and odds ratio formats.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu