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Odds, probability, edge, and CLV

The arithmetic behind every tool on the site: converting a price into a probability, spotting the bookmaker margin, and knowing what an edge does and does not promise.

Value Bets, Pro Models, the Acca Generator, and the Bet Tracker all rest on the same handful of conversions. They are worth understanding once, because after that every tool on the site reads the same way.

Price to probability

Divide 1 by the decimal price. A price of 2.00 implies 50%. A price of 1.25 implies 80%. A price of 5.00 implies 20%. That single conversion is what lets a price and a model probability be compared at all.

Decimal odds	Implied probability	Break-even hit rate
1.25	80.0%	4 wins in 5
1.50	66.7%	2 wins in 3
2.00	50.0%	1 win in 2
3.00	33.3%	1 win in 3
5.00	20.0%	1 win in 5

The bookmaker margin

Add up the implied probabilities of every outcome in a market and the total comes to more than 100%. The excess is the bookmaker margin, and it is the reason betting at random loses money over time. A market at 105% is charging you five points; a 1X2 market at 112% is charging you twelve.

Why this matters for value

An edge has to clear the margin before it is real. That is why the tools compare against the actual price offered rather than against a tidy fair price, and why a wide margin market needs a bigger model edge to be worth taking.

Edge and expected value

Edge is the gap between what the model thinks and what the price says. Expected value converts that gap into money.

If the model says 60% and the price is 2.00, the edge is ten percentage points. Expected value per unit staked is the model probability multiplied by the profit if it wins, minus the chance of losing multiplied by the stake: 0.60 × 1.00 − 0.40 × 1.00 = +0.20. Twenty percent expected return per unit, over a long run of similar bets.

The long run is longer than it feels

A genuine 20% edge at even money still loses four times in ten. Losing runs of six or seven are normal, not evidence the edge has gone. This is why staking discipline matters more than any individual selection.

Closing line value

The closing price is the market’s final answer, after all the money and all the team news. If you consistently take prices bigger than the close, you are consistently finding value before the market does — and that shows up long before profit does.

Backing 2.10 on a selection that closes at 1.90 is positive CLV, regardless of the result.

This is why Prediction Accuracy publishes average CLV next to ROI, why Pro Models pauses markets with weak closing-line coverage, and why the Bet Tracker has a closing odds field. Same idea in three places.

Accumulators and combined probability

Legs multiply. Four selections at 80% each combine to 0.8⁴, which is about 41%. The price multiplies too, but so does the bookmaker margin — once per leg. That is the honest reason accumulators are harder than they look, and why the Acca Generator always shows total probability next to total odds.