Odds Converter: Translate Between American, Decimal, Fractional, and Probability
Different books, different countries, different formats. American odds work fine for US sportsbooks; decimal odds make parlay multiplication trivial since you just multiply all legs together. This converter keeps all four representations in sync so you can paste whatever format the source gives you and get the rest instantly, including dollar payouts on your planned stake.
When each format makes the most sense
American odds are efficient for communicating relative value on US markets. +150 versus +130 is immediately intuitive for anyone who bets regularly. The limitation is parlay math - multiplying +150, -110, and +200 in American format requires conversion to decimal first.
Decimal odds make parlay math trivial. A three-leg parlay is 2.50 x 1.91 x 3.00 x stake. Every bet comparison site uses decimal internally for this reason, even on pages that display American to users.
Fractional odds remain standard on horse racing markets in the UK and Ireland. 5/1 means five dollars profit per dollar staked. They are less useful for modern sports betting math but essential when dealing with UK-facing operators.
How the synchronized fields stay consistent
All three odds formats convert exactly to and from implied probability without precision loss unless a repeating decimal rounds. The chain is: format to probability to other formats.
Bet Amount scales To Win and Payout for dollar planning but does not change implied probability or odds conversions. Enter the stake you plan to use and payout math updates alongside the odds display.
The active field drives the calculation. When you type into Decimal, American and Fraction update from that value. When you switch to American and type, Decimal updates from American. Each field is both input and output depending on which one you are editing.
Step by step: using this calculator
Click the field matching how your source quotes the price. Type the number. The other fields fill in immediately. Set Bet Amount to see the actual dollar payout on your planned stake.
To convert several prices in a row, keep Bet Amount fixed and just update the active odds field each time. No page refresh needed.
- Set Bet Amount to your planned stake.
- Click into Decimal, American, Fraction, or Probability % to match your source.
- Type the odds.
- Read To Win, Payout, and Implied Probability alongside all converted formats.
Worked example: +150 American across all formats
American +150: decimal = 2.50 (1 + 150/100), fractional = 3/2, probability = 40.0% (100 / 250). On a $100 stake: To Win = $150, Payout = $250.
Entering 2.50 in the Decimal field produces the same result. American fills to +150, Fraction to 3/2, Probability to 40.0%. Any entry point gives the same output.
Parlay context: combining +150 (2.50) and -110 (1.91) gives a two-leg parlay of 2.50 x 1.91 = 4.78 decimal = +378 American. You cannot multiply +150 and -110 directly in American format - the decimal detour is mandatory.
Decimal
2.50
Fractional
3/2
Implied probability
40.0%
Common mistakes during rapid edits
Leaving malformed values in inactive fields. If you typed a bad number into Decimal and switched to American, the Decimal field holds its last stale value until you clear it.
Expecting payout updates when Bet Amount is empty or zero. Payout depends on stake - a blank field leaves To Win and Payout at zero.
Using this converter as a no-vig tool. The converter preserves posted prices as-is. To find fair prices without margin, use the no-vig calculator with both sides of the market as inputs.
What most calculator pages skip
This calculator defaults to your local format based on region - US gets American, UK gets fractional, Australia gets decimal. When you are browsing a foreign book with the OddsGuard extension, the converter matches that book's format automatically so there is no mental translation required.