Overround in betting

Overround is how much a betting market adds up to above 100%. A market at 106% is charging you six percentage points for the right to play.

Convert every selection to implied probability and add them. Anything over 100 is the operator's theoretical hold: if it balances its book perfectly across all outcomes, it keeps that slice regardless of the result. Tight markets — Premier League match odds at big books — run 102% to 104%. Obscure markets, correct score and long-shot specials can run 115% or worse.

Overround = sum of (100 / odds) for every outcome. Bookmaker hold ≈ (overround - 100) / overround.

Over 2.5 at 1.85 and Under 2.5 at 1.85 imply 54.05% each, totalling 108.1%. That is an 8.1% overround on a coin-flip market: to break even you need to win 54.05% of the time, not 50%. Move to a book pricing both sides 1.95 and the requirement drops to 51.3% — the same bet, a far lower bar.

Margin is the fee you pay per bet, and it compounds faster than any losing run. A bettor giving away 8% per market needs an extraordinary edge just to reach break-even; the same bettor on 3% markets only needs to be slightly better than average.

Nigerian operators often run wider margins on local leagues and jackpot markets than on the Premier League, because they know volume follows familiarity. Price-check NPFL and jackpot legs especially hard — the gap between best and worst is widest exactly where the crowd is not looking.

• Judging a book by its Premier League prices and assuming its correct-score margins are equally fair.
• Ignoring margin in accumulators, where it compounds on every leg.
• Confusing the overround with the bookmaker's actual profit; it is the theoretical hold on a balanced book, not guaranteed income.