Five words, one idea
The vocabulary is cluttered because the concept is central. Vig (vigorish) and juice are the informal names for the commission. Overround and book percentage describe it from the probability side — how far a market's prices sum past 100 percent. Margin is that same cut expressed as a percentage of the book. Hold is the money the book actually keeps once bets are settled. One idea, five labels, and the only distinction that matters is theoretical versus realised.
The theoretical side comes straight out of the implied probability calculation. Sum the raw implied probabilities of every outcome, see how far past 100 percent you land, and you have measured the book's built-in edge before a single bet is placed.
Margin on a two-way market
Start with the canonical American price of −110 on both sides. Its decimal equivalent is 1.909, and the margin falls out in three steps.
# −110 both sides to decimal 1.909 each p_a = 1 / 1.909 = 0.5238 p_b = 1 / 1.909 = 0.5238 book_pct = p_a + p_b = 1.0476 # 104.76% # overround (percentage points) overround = 104.76% − 100% = 4.76 points # margin as a share of the book margin = (book_pct − 1) / book_pct = 0.0476 / 1.0476 ≈ 4.5%
Two figures, two conventions. The overround of 4.76 points is the book-percentage view. The margin of about 4.5 percent expresses the same cut as a fraction of the total book, which is the number most directly comparable to a hold. Both come from the prices alone — no bet volumes required — which is why they are called theoretical.
Margin on a three-way market
Nothing changes but the number of terms. A soccer 1X2 market has three outcomes, so you sum three implied probabilities. The figures below are illustrative.
# illustrative three-way prices (decimal) home 2.40 to 1/2.40 = 0.4167 draw 3.30 to 1/3.30 = 0.3030 away 3.10 to 1/3.10 = 0.3226 book_pct = 0.4167 + 0.3030 + 0.3226 = 1.0423 margin = 0.0423 / 1.0423 ≈ 4.1% # of the book
More outcomes usually means the margin is spread across more prices, but the method is identical: reciprocal, sum, compare to 100 percent. To recover each outcome's fair probability you normalise — divide each side by the book percentage — exactly as in the vig remover.
Margin versus hold
Here is the distinction that trips people up. Margin is what the prices imply. Hold is what the book actually banks. They agree only when the book's exposure is balanced — when the money on each outcome is proportioned so the book pays the same regardless of which side wins.
The practical takeaway: margin is computable from a screen and always available; hold is an after-the-fact accounting figure you cannot see as a bettor. When you compare books, you are comparing margins.
What juice does to break-even
The margin is not an abstraction — it sets the win rate you need just to stay level. At even money you break even by winning half your bets. Every cent of juice raises that bar.
# break-even win rate at decimal price D breakeven = 1 / D # even money D = 2.000 to 50.00% # −110 D = 1.909 to 52.38% # −115 D = 1.870 to 53.48% # −120 D = 1.833 to 54.55%
| American | Decimal | Break-even win rate |
|---|---|---|
| +100 (even) | 2.000 | 50.00% |
| −110 | 1.909 | 52.38% |
| −115 | 1.870 | 53.48% |
| −120 | 1.833 | 54.55% |
Read the gap between −110 and −120: the required win rate climbs from 52.38 to 54.55 percent. That two-point jump is the difference between a beatable price and a punishing one, and it is paid on every bet. Widening juice is the quietest way a book protects itself, and spotting it is why comparing margin across books on the same market is one of the highest-return habits a bettor can keep. It also raises the bar for any claimed edge — the expected-value guide measures your number against the fair line precisely because the juice is standing in between.