Closing line value calculator: grade a bet against the close

A closing line value calculator compares the price you got with the price the market settled on at close, after taking the sportsbook's margin out of that closing price. Beat the close and you have positive CLV. It is a way to grade a bet before the game is played, which matters because one result tells you almost nothing.

The formula

One documented version, from SharpAPI's CLV reference, is:

CLV % = (closing no-vig probability x entry decimal odds - 1) x 100

Its docs say positive CLV means the price beat the close, that the closing price is devigged (they use the power method), and that the reference book is typically Pinnacle. They also warn that comparing against a fallback reference gives negative CLV that should not be read as edge.

Read the formula this way: the closing no-vig probability is the market's final estimate of the true chance. Multiply it by the decimal payout you were offered. If the product is above 1, you were paid more than the final estimate said you should be.

A worked example

Hypothetical prices, not results. You bet a side at -110 (decimal 1.9091, implied 52.38 percent). The reference book closes at -125 / +105.

1. Implied probabilities of the close: 55.56 percent and 48.78 percent, a total of 104.34.
2. Remove the margin by dividing by the total: 53.25 percent and 46.75 percent.
3. CLV % = 0.5325 x 1.9091 - 1 = +1.65 percent

If you devig the closing line with the power method instead, the fair probability comes out near 53.46 percent and CLV near +2.06 percent. Same bet, slightly different answer (a 2017 comparison of margin-removal methods favored the power method), which is why the method should be fixed before you start tracking.

Price CLV versus probability CLV

People report CLV in two ways.

Price-based. The formula above. It is a percentage return against the closing fair price. It uses the payout you actually got, so it reflects long odds fairly.

Probability-based. The difference in percentage points between the closing fair probability and your entry implied probability. In the example that is 53.25 - 52.38 = +0.87 points.

The two always agree on sign but they scale differently. A one-point move on a +400 underdog is a much bigger percentage change in price than a one-point move on a -400 favorite. If you compare bets across different odds ranges, price-based CLV is the fairer yardstick. Probability points are easier to read on a single market.

One mistake to avoid: comparing your entry implied probability to the closing line's implied probability without devigging the close. In the example that gives 55.56 - 52.38 = 3.18 points, nearly four times the honest figure, because the close still carries the book's margin.

What CLV does and doesn't tell you

CLV is a quality check on the price, not a profit statement. Researchers who tested odds-based strategies used probabilities implied by public odds to look for mispriced bets, including a ten-year simulation on closing odds and five months with real money (arXiv, 2017), and the same abstract says the industry answers successful clients with "discriminatory practices". That is one reason to track whether your prices hold up against the close rather than just your win-loss.

• A positive average over many bets is a good sign you are buying prices better than the market ends up paying. It is not proof, and it does not promise profit.
• A single bet's CLV is noisy. The market moves for reasons that have nothing to do with you.
• CLV depends on the closing source. A close from a sharp book and a close from a soft book mean different things.
• Bets you can't get closing prices for (thin props, alternate lines) are hard to grade.

Betting odds are informative as forecasts: published work finds odds often beat mathematical models (PLOS ONE). That is the case for using the close as a benchmark at all.

Steps to track it yourself

1. Record the price, book and timestamp when you bet.
2. Record the closing prices on both sides at your chosen reference book.
3. Devig the close with one method every time. The devig calculator page compares the common ones.
4. Compute CLV for each bet, then average across the bets in a category (sport, market type, book).
5. Look at a few hundred bets before drawing a conclusion, and look at spread as well as average.

A spreadsheet can do this. The part that takes time is collecting closing prices, which is the part software is for.

How quant+ handles it

The bet tracker is the bet journal: it grades bets and measures closing-line value against the closing price on the board. The line movement tracker shows the open, the close and every tick between them, so you can see when your price was the best one available. The fair odds calculator page explains how the fair price under each board row is built.

Limits

• CLV measures price, not whether the bet won.
• It is only as good as the closing source and the devig method.
• Small samples mislead.
• It says nothing about whether you can still get down at that price. Books limit some accounts.

quant+ shows these numbers for information only. It doesn't place bets or connect to sportsbook accounts.

Quant+ is analytics for informational purposes. 21+. If you or someone you know has a gambling problem, call 1-800-GAMBLER.