Sportsbook Overround & Book Percentage
How to measure the displayed margin built into a complete betting market.
Convert every mutually exclusive outcome to implied probability and add them. If a two-way market totals 104.71%, the displayed overround is 4.71 percentage points.
Two-way example
At decimal 1.91 on each side, each price implies about 52.36%. Together they total about 104.71%.
Not the same as guaranteed sportsbook profit
Overround is a price-structure measure. Actual operator results depend on stakes, liabilities, outcomes, trading and promotions.
Market completeness matters
Only sum outcomes that form a complete mutually exclusive market under the same settlement rules.
Compare like with like
A market with lower overround is generally priced more tightly, but individual outcome prices can still be better or worse at different books.
Use normalization carefully
Removing margin proportionally gives a useful no-vig estimate but does not prove the resulting probabilities are objectively fair.