Why odds formats do not change the bet

A price of 2.50 is a price of 3/2 is a price of +150. All three describe the same offer: risk one unit, and if it lands you hold two and a half. The choice between them is a choice about which one you read without stopping to think.

#The one place formats do differ

Fractional odds round. A book showing 11/10 and a book showing 2.10 are offering the same thing, but a book showing 11/10 when the true price is 2.12 has rounded against you and the fraction gives you no way to see it. This is why anybody comparing prices across books should compare in decimal even if they read in something else, and why this product converts rather than stores a format.

American odds have a discontinuity at even money that trips people up. +100 and -100 are the same price, and there is nothing between them. A move from +105 to -105 is a small move that looks like it crossed something important.

#Why we let you choose

A reader in Lyon and a reader in Ohio are looking at the same board and reading two different alphabets. Forcing either into the other's notation adds a translation step to every glance, and a translation step is where mistakes live. So the format is a setting, defaulting to whatever is normal where you are, and every figure in the product follows it.

None of this touches the arithmetic. Whatever notation is on screen, the thing being compared is the gap between our number and the price, and that gap is measured in probability.

#What this does not tell you

Format has no bearing on whether a price is good. A beautifully readable +150 at a book charging 8% margin is worse than an awkward 13/8 at a book charging 2%. Readability is a convenience, not a signal.