Odds Calculator
Convert between probability and odds, and see odds in favor and against an event side by side.
Odds versus probability
Probability expresses how likely an event is as a share of all outcomes (for example, 25%). Odds instead compare the favorable outcomes directly to the unfavorable ones (for example, 1 to 3). The two describe the same underlying chance but are written differently, which often causes confusion.
How this calculator works
Choose whether you already know the probability or the odds ratio. If you enter a probability, the calculator converts it into an equivalent odds-for-to-against ratio. If you enter odds as two numbers (for and against), it converts them into a probability using probability = for / (for + against). It also shows decimal odds, a format commonly used to express payout multiples.
This calculator is for general educational and planning use, such as understanding statistics, games of chance, or risk descriptions, and is not gambling or financial advice.