vig-removal

name	vig_removal
description	Remove the bookmaker margin (vig/overround) to estimate fair probabilities and spot value.
triggers	["vig","overround","juice","fair price","fair probability","fair odds","true price"]

Removing the vig

A bookmaker's quoted prices imply probabilities that sum to MORE than 1 — the excess is the margin (vig / overround / juice). To estimate what the market really thinks, remove it.

Procedure

1. Collect the decimal odds for every selection in the same market at one bookmaker (all runners / both sides). Partial markets give wrong answers.
2. Call the vig_removal tool with those prices. It returns:
   • overround — e.g. 1.052 means a 5.2% margin
   • fair_probabilities — each selection's implied probability normalised to sum to 1
3. To compare value across books: get the fair probability from the sharpest market available (Pinnacle / Betfair exchange when present — lowest overround), then call expected_value with that probability against each book's offered odds.

Rules

• Never average odds across books before removing vig — remove per book, then compare.
• A two-way 1.90/1.90 market is ~5.26% vig and 0.50/0.50 fair — a useful sanity check.
• If you cannot get the FULL market at one book, say so; do not normalise a partial set.
• Report the overround alongside any "fair" number so the user sees the margin you removed.