Paste the prices for every outcome of a market and get the hold — the share the book keeps — along with the no-vig fair price behind each one. Works for two-way markets and for three-way ones like soccer.
Every price implies a probability. Decimal odds of 2.00 imply 50%; American odds of −110 imply 52.4%. Add up the implied probability of every outcome of a real market and you get more than 100% — and you should, because the excess is how the book gets paid. That excess is the hold.
Lower hold is strictly better for you: it is the headwind every bet at that book runs into before skill matters at all. It is also how you compare books honestly — a book with a flashy price on one side and a terrible one on the other is not a cheap book, and the hold is the number that says so.
If the prices you paste come from different books, the total can land under 100%. That is a negative hold, and it means backing every outcome guarantees a profit — an arbitrage. No single book prices itself into one; it only appears when two books disagree.