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A convincing prediction is not automatically a well-priced wager.
A team can look certain to win—strong recent form, a favourable matchup, an injured opponent—and still be a poor bet at the posted odds. The question is not simply whether the selection wins; it is whether its chance of winning is higher than the price implies.
That distinction matters because even sound bets lose regularly. A wager with a genuine edge can fail tonight, while an overpriced long shot can land by luck. Expected value judges the decision before the result: across many similar bets, did the odds offer enough return to cover the losses? Treating each wager as one entry in a long series keeps attention on price, probability, and discipline rather than memorable wins or painful near-misses.
- A 60% chance needs odds better than 1.67 decimal to have positive expected value, before any bookmaker margin.
Expected value measures the price of a bet
- Expected value (EV)
The average profit or loss a stake would produce if the same wager, at the same odds and true probability, could be repeated many times.
- Positive EV
The estimated probability is better than the odds imply. Results will still vary, but the price is favorable over a large sample.
- Neutral EV
The implied price matches the estimated chance of winning. Before fees or bookmaker margin, the long-run average is roughly break-even.
- Negative EV
The odds pay less than the bet’s estimated risk warrants. A win can occur, but repeating that choice is expected to lose money.
A positive-EV ticket can lose tonight; a negative-EV ticket can win. Neither outcome proves the original decision was good or bad.
EV asks a different question: given the probability estimate and the offered odds, was this a price worth taking repeatedly?
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A personal win estimate
Assign a realistic chance that the selected outcome wins before looking at whether the price feels attractive. This estimate can come from form, injuries, matchup data, and relevant context, but it remains a judgment rather than a certainty.
NeededA stated probability based on information beyond the listed odds.Do not rely onTreating confidence or a recent winning streak as a probability. -
The actual payout
Record the offered odds and stake, then convert them into the profit if the bet wins and the amount lost if it fails. Expected value needs both sides of that trade.
NeededNet profit on a win and full stake loss on a loss.Do not rely onUsing a headline payout without checking the odds format or stake. -
A separate benchmark
Sportsbook odds imply a probability, but that number is the market price, usually with margin built in. Reusing it as the win estimate makes the comparison circular and cannot reveal a genuine edge.
NeededAn independently formed probability compared against the implied probability.Do not rely onAssuming implied probability is the true chance of winning. -
A margin for uncertainty
When the estimate is shaky, round it down or require a larger gap between estimated chance and implied chance. Small apparent advantages often vanish when assumptions are slightly wrong.
NeededConservative estimates, especially for thin data or volatile events.Do not rely onBetting a narrow edge supported by uncertain assumptions.
Write the win probability before converting the odds to implied probability. If both figures end up nearly identical, there is probably no usable edge—especially after allowing for estimation error and sportsbook margin.
Convert odds into payouts and probabilities
Odds contain two separate figures: the return on a winning ticket and the market’s break-even win rate. Keeping net profit separate from total return prevents a frequent EV mistake. A $10 bet at decimal 2.50 returns $25 in total, but its profit is only $15; EV uses $15 for a win and -$10 for a loss.
Use the matching conversion
For a stake of S, the common formats work as follows:
| Odds format | Net profit | Total return | Implied probability |
|---|---|---|---|
| Decimal D | S × (D − 1) | S × D | 1 ÷ D |
| Fractional A/B | S × A/B | S × (1 + A/B) | B ÷ (A + B) |
| American +X | S × X/100 | S × (1 + X/100) | 100 ÷ (X + 100) |
| American −X | S × 100/X | S × (1 + 100/X) | X ÷ (X + 100) |
For example, decimal 2.50 implies 40% (1 ÷ 2.50). That is the approximate break-even rate at that price, before any bookmaker margi