THE MATHS, MADE CLEAR
How it works
Positive American odds show profit for a 100-unit stake. Negative American odds show the stake needed to profit 100 units. Fractional odds describe net profit relative to stake; decimal odds include the returned stake. Conversions use the unrounded internal decimal price. Display values are rounded; repeating fractions may be approximated and labelled.
Implied probability = 1 ÷ decimal odds; fractional odds = (decimal odds − 1) / 1
A worked example
Decimal 2.50 equals fractional 3/2 and American +150. The implied probability is 40%. A winning 100-unit stake returns 250 including the original stake. Decimal 1.50 equals 1/2, −200 and an implied 66.67%.
Understand the assumptions.
These are educational calculations, not predictions or recommendations. Display amounts are rounded to two decimal places; calculations retain internal precision.