Guide
Guide · 5 min read
Removing the vig to find a fair price
If the implied probability of a price is a little too high because of the fee, the natural next question is: what is the fair chance underneath? Taking the fee out is called removing the vig, or de-vigging. It is how BetChecker estimates the true chance behind a price, and you can do a simple version by hand.
The idea in one line
Both sides of a market should add up to 100%, but with the fee they add up to more. So you shrink both sides by the same proportion until they total exactly 100%. What is left is a fair estimate of each side's chance, with the fee stripped out.
Example: -120 on one side, +100 on the other
-120 implies 120 divided by 220, which is 54.5%.
+100 implies 100 divided by 200, which is 50.0%.
Together: 104.5%. The 4.5 points over 100 is the fee.
Divide each by 104.5%: 52.2% and 47.8%. Now they add up to 100%.
So the fair chance for the -120 side is about 52.2%, not 54.5%.
Why this is better than the raw price
The raw implied number, 54.5%, is the chance the bet needs to break even. The de-vigged number, 52.2%, is a fair estimate of the chance it actually has. The gap between them, about 2.3 points here, is the fee working against you. Seeing both numbers side by side is the whole point: one is the bar, the other is the reality.
A note on long shots
There is more than one way to remove a fee, and the methods agree closely on even games but disagree on long shots, where the fee is spread unevenly. A simple proportional split, like the one above, can flatter a big underdog. That is why BetChecker works it out more than one standard way and uses the result that is least flattering to your side, so we never call a price better than it really is.
What the fair price does not promise
A fair chance is an estimate, not a guarantee. It leans on the idea that the market, taken as a whole, prices games about right. That holds up well on average over many bets, which is what the fair price is built to measure. It says nothing about how any single game will end. No method can, and anyone who claims otherwise is selling something.
You can sanity-check any de-vig in one step. Add your two fair numbers back together. If they come to 100%, the arithmetic is sound. If they do not, something slipped. It is a small habit that catches most mistakes, and it works no matter which method you used to remove the fee, because every honest method has to land both sides on a total of exactly 100%.
De-vigging shrinks both sides back to 100% to reveal the fair chance under a price. Compare it with the break-even chance, and the gap is the fee you are being charged.
For entertainment and education. Nothing here predicts results or recommends a bet.