Bookmaker margin
from the line odds
2 outcomes
3 outcomes
Mathematical (overround)
—
sum of probabilities − 100%
Bookmaker's (real)
—
bookmaker's share of the bank
Mathematical margin — by how much the sum of inverse odds exceeds 100% (the classic overround).
Bookmaker margin — the real share the bookmaker keeps when stakes are spread equally across all outcomes (this is usually what bookmakers mean by the line margin; it is always smaller than the overround).
Bookmaker margin — the real share the bookmaker keeps when stakes are spread equally across all outcomes (this is usually what bookmakers mean by the line margin; it is always smaller than the overround).
Stake distribution (arbitrage)
how much to stake on each outcome so the profit is the same
2 outcomes
3 outcomes
System M of N
winnings when outcomes partly match
Odds converter
decimal ⇄ American ⇄ fractional
Enter a value in any field and the other two recalculate automatically.
Bookmaker margin calculator
Bookmaker margin is the percentage the bookmaker builds into the line. If you add up the inverses of the odds of all outcomes (1/odds), a fair line gives exactly 100%. Anything above 100% is the margin.
Example: for a match with two outcomes, the odds are 1.91 and 1.91. 1/1.91 + 1/1.91 = 104.7%, so the margin is 4.7%. The lower the margin, the better the line is for the bettor. The calculator computes the margin for two and three outcomes and shows probabilities and odds without the margin.