Converting between the three formats

Decimal is the hub. From fractional, divide and add one: 5/2 becomes 3.50. From a positive American price, divide by 100 and add one: +250 becomes 3.50. From a negative American price, divide 100 by the price and add one: −200 becomes 1.50. Going the other way, subtract one from the decimal and you have the fractional price as a decimal ratio; if that result is one or more the American price is it multiplied by 100 with a plus sign, and if it is less than one the American price is −100 divided by it.

Every format encodes the same single quantity — how much the payout multiplies the stake — and they differ only in what they include and what they measure against. Routing everything through decimal means you learn two conversions rather than six, and decimal is the only one of the three where comparison is just reading the larger number.

Books round, and they round in their own favour more often than not. A true 1.909 will often appear as 1.90, and a 3.4995 as 3.49 — small on one bet, and it is a real cost applied to every bet you place at that book.

That is also the expensive part. Sloppy converting is nearly always in the flattering direction, because the memorable shortcuts drop the stake. '+250 is 2.5 times my money' quietly becomes 3.5 times when the stake is added, and nobody ever misremembers it the other way.

What to do with it. Do the round trip once for any price you are about to bet: convert out, convert back, and check you land where you started.

The bet calculator does all three conversions at once, if you would rather read the number than work it out.

Work it out. The odds converter turns any American, decimal, fractional or percentage price into the other three.