A value bet is a bet where the odds on offer are bigger than the true chance of the outcome deserves. In other words, the bookmaker is paying more than a fair price. Over many bets like that, you'd expect to come out ahead on average.
The key word is price. Value has nothing to do with how likely the bet is to win. A player at 1.50 to have a shot on target can be poor value if his real chance is 60%, and a player at 12.00 to score a header can be value if his real chance is 10%.
Example (hypothetical): you estimate a player has a 40% chance to score, so his fair odd is 1 / 0.40 = 2.50. A bookmaker offers 2.80. Expected value is 0.40 x 2.80 - 1 = +0.12, or +12% of your stake on average. At 2.30 the same bet would be about -8%.
The hard part is the estimate. If your 40% is really 33%, the 2.80 isn't value at all. That's why value bettors rely on a model, a sharp bookmaker's price with the margin removed, or a tool that builds fair odds for them, and why they keep records to check whether their estimates hold up.
Even with genuine value, losing runs are normal. Expected value is a long-run average. Stake sizes should be small enough to ride out the bad spells.
Frequently asked questions
What does value bet mean?
It means the odds on offer are bigger than the fair odds for that outcome, so the bet has positive expected value. It says nothing about whether the bet is likely to win.
How do you find value bets?
Estimate a fair odd for the outcome, then compare it with what bookmakers are offering. If the bookmaker's odd is bigger than your fair odd, the bet is value, as long as your estimate is right.
Can a value bet lose?
Yes, often. Value is about the average result over many bets. Any single value bet can lose, and losing runs are a normal part of value betting.