Every price a bookmaker posts is slightly worse than the true chance of the thing happening. The gap is the hold — also called the margin, the overround or the vig — and it is how the business makes money whichever way the game goes.
How to calculate it
Convert each price to an implied probability by dividing 1 by it, then add them up. A market with no margin at all would sum to exactly 1.00, or 100%. Anything above that is the hold.
Take a match priced at $1.90 and $1.90:
- 1 ÷ 1.90 = 0.5263
- 1 ÷ 1.90 = 0.5263
- Total = 1.0526, so the hold is 5.26%
That is a completely ordinary two-way NRL market. Now the same match, if you take the best price on each side from two different bookmakers — say $1.95 and $2.02:
- 1 ÷ 1.95 = 0.5128
- 1 ÷ 2.02 = 0.4950
- Total = 1.0078, so the hold is 0.78%
Nothing about the match changed. The margin fell by more than four fifths purely because each side came from whichever book priced it best.
What that difference is worth
Hold is a percentage of everything you stake, so it scales with turnover rather than with how often you win. On $1,000 put through both sides of a market:
| Hold | Cost per $1,000 |
|---|---|
| 5.26% (one book, typical) | $52.60 |
| 2.00% | $20.00 |
| 0.78% (best of two books) | $7.80 |
If a market ever sums to below 100%, the bookmakers have priced it in your favour and backing both sides returns a profit whatever happens. That is arbitrage, and it is rare and short-lived — see the arbitrage guide.
Two things that trip people up
An exchange price is not what you collect. Betfair quotes before taking its commission on winnings — usually 5%. A $2.10 exchange price really returns about $2.045, so it can look like the best price on the board while paying less than a bookmaker offering $2.08. Any honest comparison has to take the commission out first.
Low hold is not free money. Finding a 0.5% market does not mean you profit — it means you lose less if you back both sides. It is useful when turning money over is the actual goal, such as clearing a bonus-bet turnover requirement, rather than as a strategy for making money on its own.
Why it matters more than picking winners
A margin you pay on every bet compounds quietly in a way a losing week does not. Someone betting through 5% markets is starting every bet meaningfully behind; someone taking the best available price on each bet is starting much closer to even. Neither has predicted anything. That is the point — this is the part of the result you control.