Closing line value (CLV) explained

Closing line value (CLV) compares the price you bet at with the market's final price before the event starts. If you consistently get better prices than the close, you were probably betting before the market moved your way. That's a useful sign of skill, it's what sportsbooks watch, and it's still not proof you'll make money.

The definition

The closing line is the last price before betting closes. The Massachusetts Gaming Commission, which asked sportsbooks for CLV data, describes it as a measure of how "good" or "sharp" a player is, based on whether they bet at better odds than the odds at which the wager closes.^[1]

How to calculate it

The cleanest comparison is against the no-vig closing price, so the sportsbook's margin doesn't flatter or penalise you.

Example: you bet Team A at 2.20. At the close, the market is Team A 2.00, Team B 1.83 (-120).

1. Implied probabilities at the close: 50.00% and 54.55%, a total of 104.55%.
2. No-vig probability of Team A: 50.00 ÷ 104.55 = 47.83%, or fair odds of 2.091.
3. CLV = your odds ÷ fair closing odds − 1 = 2.20 ÷ 2.091 − 1 = +5.2%.

If the closing line were the truth, that bet had about +5.2% expected value. That's why CLV is often used as a quick estimate of EV. The no-vig calculator handles step 2.

Why sportsbooks care

CLV identifies the bettors whose prices the market later agrees with. In Massachusetts, regulators' data showed that players who consistently beat the closing line were more likely to have their limits lowered, and those who didn't were more likely to have them raised.^[1] For a positive-EV bettor, strong CLV and account limits tend to arrive together. See Why sportsbooks limit winning bettors.

Why positive CLV isn't a guarantee

Two caveats matter more than any formula:

• The close isn't the truth. It's the market's last estimate. In thin markets, or at books that move slowly, the closing price can still be wrong.
• You have to beat the margin, too. Economist Karl Whelan, analysing NBA moneyline bets, found that bets with positive CLV did better than bets without it, but that positive CLV alone did not guarantee a profit; bets had to beat the closing line by enough to overcome the sportsbook's margin.^[2]

Use CLV as a diagnostic over hundreds of bets, alongside your actual results, not as a substitute for them.

Practical tips

• Record the price, time and sportsbook of every bet, and the closing prices for the same market.
• Compare against a sharp, liquid market's no-vig close where you can.
• Average CLV over many bets; individual bets are noisy.
• Don't mistake CLV on tiny, unbettable limits for an edge you can scale.