How to read a BAI8 price that is days old

Every BAI8 card shows the best price we saw and the time we saw it. Sometimes that time is days ago, and that is a real weakness: an edge measured against a price that has since moved may no longer exist. The fix takes ten seconds. Ignore our edge, take our fair price, and compare it with the price you can get now. If today's price is higher than our fair price, the gap is still there on our numbers. If it is lower, it is gone.

Why the price can be old

Our number and the price come from two different places. The number is the result of the research on a fixture and is published once that research is done, as described in how BAI8 prices a fixture. The price is the best quote we captured across the bookmakers we compare, stamped with when it was captured.

On 8 October the gap between the two was plain. Five of the six cards on our Desk carried best prices quoted between 23:30 and 23:33 UTC on 4 October, while the assessments themselves were published between 5 and 8 October. For a weekend match, that can be a lot of news: this week it spanned the end of an international break.

We would rather show you an old price with its time than a price with no time at all. But we will not pretend an old price is today's.

The ten-second check

You need two numbers: our fair price and the price in front of you.

Take Lyon at Lens. We give Lyon a 37.7% chance, so our fair price is 2.65 (one divided by 0.377). The card's best price was 2.92, from 4 October.

• If you can get 2.80 now, that implies 35.7%. Our 37.7% is still 2.0 points higher. The gap is smaller, but it is there.
• If the best you can get is 2.60, that implies 38.5%. The price is now shorter than our fair price, and on our numbers there is no edge at all.

That is the whole method. The edge in points is our chance minus one divided by the price. The fair price is the break-even line. Above it, positive. Below it, not. The idea is explained more fully in what a positive edge actually means.

What we still have to fix

An edge printed against a stale quote can mislead anyone who reads the card quickly. Showing the quote time is the minimum. Better would be a fresher quote close to publication, or a clear flag when a quote is more than a day old. Until then, treat our fair price as the number that matters and the quoted price as history.

What this does not tell you

It does not tell you our probability is right; the check only tells you whether today's price still disagrees with it. It does not account for the margin a bookmaker builds into a price you are offered. And it says nothing about whether a price will be there by the time you look. BAI8 never places bets, so none of these prices is an offer from us.