Definition
Synthetic hold is the margin created when you combine the best available prices from different sportsbooks on every side of the same market.
Formula for a two-outcome market:
synthetic hold = implied probability of side A + implied probability of side B - 100%
For American odds, implied probability is:
negative odds: odds / (odds + 100)
positive odds: 100 / (odds + 100)
Worked Example
One book lists Team A at -105. Another book lists Team B at -102.
Team A implied probability:
105 / (105 + 100) = 51.22%
Team B implied probability:
102 / (102 + 100) = 50.50%
Synthetic hold:
51.22% + 50.50% - 100% = 1.72%
That combined market has a 1.72% hold using the best prices available across those books. If both sides were -110, the hold would be:
52.38% + 52.38% - 100% = 4.76%
Why It Matters
Synthetic hold helps a bettor see whether shopping lines has reduced the book’s margin enough to make a market worth modeling. Lower synthetic hold gives projections a cleaner price to compare against.