Fair price vs best price on a BAI8 card

A fair price is what our chance is worth in odds. A best price is what a bookmaker is actually offering. When the best price is longer than the fair price, the card shows a positive edge. That gap is the only reason a card exists; who we think wins is secondary.

The two numbers

• Fair price = 1 divided by our chance. 50% is 2.00. 52.2% is 1.91.
• Best price = the longest price we saw for that side, with the bookmaker and the time it was quoted.
• Edge = our chance minus the chance the best price implies, in points.

Three of today's cards

Fixture	Side	Our chance	Fair price	Best price	Implied by best	Edge
Seahawks v 49ers	49ers	52.2%	1.91	2.56, Betfair	39.1%	+13.2 pts
Malaga v Espanyol	Espanyol	38.9%	2.57	2.82, Betfair	35.5%	+3.4 pts
Blue Jackets v Penguins	Penguins	51.3%	1.95	2.06, Betfair	48.5%	+2.7 pts

Take the 49ers. We say 52.2%, so our fair price is 1.91. Betfair offered 2.56, which implies 39.1%. The gap is 13.2 points. Run the same sum on the others.

Why the time stamp matters

A best price is a snapshot. The Espanyol 2.82 was quoted on 4 October, five days before kick-off. The Penguins 2.06 was quoted on the morning of the game. An old quote may have moved, which is why every card shows when it was seen. The full routine is in how to read a BAI8 price that is days old.

Fair is not the same as no margin

The bookmaker's price carries a margin. Our fair price does not. That is why a fair price can look generous next to the market even when there is no edge. For how much the margin takes, see what the bookmaker's margin really costs you.

What this does not tell you

It does not tell you our chance is right. A fair price is only as good as the number behind it. And a positive edge says the price looks long on our estimate, not that the side will win.