Odds Converter

Sportsbooks around the world quote prices in three different formats. A UK Saturday-afternoon bookie will write 5/1 on his board; the same horse on Pinnacle is shown as 6.00; the same line on a US sportsbook reads +500. They all describe identical probabilities, but the eye gets used to one and stumbles over the others. The converter takes any of the three as input and shows the other two instantly, plus the implied probability and the return on a £10 stake.

This matters when shopping around multiple bookmakers, when discussing a tip with someone who uses a different format, or when reading betting analysis written for a US, European or UK audience. Three taps in the converter is faster than doing the maths in your head and removes the off-by-one mistakes that creep in around the evens line (where decimal and American both flip sign and direction).

Decimal to fractional: subtract 1 from decimal, then express as a clean fraction. 3.5 decimal becomes 2.5/1, simplified to 5/2. Decimal to American: if decimal is 2.0 or higher, multiply (decimal minus 1) by 100 and prefix with plus. If lower than 2.0, divide -100 by (decimal minus 1). 1.5 decimal becomes -200 American; 4.0 decimal becomes +300 American.

Implied probability is the cleanest sense-check across formats: 1 divided by decimal odds. A bet at 4.0 has 25% implied probability. At 3/1 fractional, same probability. At +300 American, same probability. If your honest estimate of the actual chance the bet wins is higher than the implied probability, it is a value bet; if lower, the bookmaker has the edge and you should pass.

A few benchmarks worth memorising: evens (1/1, 2.0, +100) means 50% probability and equal profit to stake. Hot favourite (1/4, 1.25, -400) means 80% probability; rare in singles, common in heavy-favourite tennis or football lines. Long shot (10/1, 11.0, +1000) means 9% probability; classic Cheltenham handicap or outright market price. True outsider (50/1, 51.0, +5000) means 2% probability; lottery-territory.

Knowing these intuitively turns the converter into a sense-check rather than a calculator. If a bookie is offering 33/1 on something you reckon is a 1-in-10 shot, that is a value bet. If they are offering 5/4 on something you think is genuinely 50/50, you are paying their margin. The [accumulator calculator](/accumulator-calculator) and [betting odds calculator](/betting-odds-calculator) both use the same odds engine, so anything you sense-check here flows through cleanly to combined-bet maths.

Evens is a special case because it is the boundary between odds-on and odds-against. Decimal 2.0 = fractional 1/1 = American +100 = 50% probability. Anything below decimal 2.0 (like 1.5) is odds-on, where the stake is more than the potential profit; in American this flips to a negative number. Anything above decimal 2.0 is odds-against, with profit larger than stake; American switches to a positive number.

Be careful with very short odds (1.05, 1.10) common in heavy-favourite betting. The fractional reads as 1/20 or 1/10 and the American reads as -2000 or -1000, both ugly. The numbers look strange but the implied probabilities (95%, 91%) are intuitive. The reverse is also true: very long shots (101.0 decimal) read as 100/1 fractional or +10000 American. Both are mathematically fine but psychologically dramatic.