Bookmaker margin on a two-way NBL market

Use one complete quoted pair

For a two-outcome NBL head-to-head market, take the two teams' decimal prices from one bookmaker at one capture time. Divide one by each price, add the resulting fractions and subtract one. The amount above zero is that quoted pair's overround.

The same arithmetic can apply to a complete over and under pair at the same total line, subject to market terms. Over 174.5 and under 175.5 do not form a clean two-outcome pair; their numbers differ.

Margin and selection price answer different questions

A lower overall margin means the pair of quotes has a smaller implied total. It does not guarantee the best payout on the particular team or side you want. To shop one selection, compare that same selection and line directly across bookmakers.

Do not combine the best NBL home price from Book A with the best away price from Book B and call the result either book's margin. That cross-book calculation is a different measure.

Record the market and time

NBL lines and prices can change. A reproducible comparison names the fixture, market, both sides, bookmaker and capture time. If a side is missing, there is no complete pair to calculate.

• One bookmaker, one NBL fixture and one snapshot.
• Both sides of the same two-way market.
• Calculate before rounding and keep payout shopping separate.