What expected value means
Expected value, usually shortened to EV, is the average amount a bet would win or lose per dollar staked if you could place it an enormous number of times under identical conditions. It is not a prediction of what happens on the next bet. It is a statement about the price: whether the payout you are offered is generous or stingy compared with how often the outcome actually happens.
That distinction is the whole point. A bet with positive expected value can lose — most of them lose a large share of the time. A bet with negative expected value can win. EV only shows up reliably across many bets, which is why it is the number serious bettors, and sportsbooks, care about most.
The formula
You need two things: a probability that the outcome happens, and the payout the price offers. Convert the price to decimal odds first (a $1 stake at decimal odds of 2.00 returns $2.00, including the stake). Then:
EV per $1 = probability × (decimal odds − 1) − (1 − probability)
The first part is what you win on average when the bet lands; the second is what you lose on average when it doesn't. If the result is above zero, the price pays more than the outcome's risk warrants. If it is below zero, the price is short.
A worked example
Suppose a forecast gives a team a 55% chance to win, and the best available price is +100 — even money, decimal odds of 2.00.
EV per $1 = 0.55 × (2.00 − 1) − 0.45 = 0.55 − 0.45 = +$0.10
On average, each dollar staked at that price would return ten cents of profit over a large number of identical bets. Now change only the price to −130 (decimal 1.769). The same 55% forecast gives 0.55 × 0.769 − 0.45 = −$0.027: a small negative, because −130 only breaks even if the team wins 56.5% of the time. Same team, same chance of winning — a different price turns the decision around.
This is why SharpDeck shows the model's probability and the best price side by side. The winner and the value are two separate questions.
Where the probability comes from
The formula is only as good as the probability you put into it. If you guess, the EV you calculate is a guess too. A forecast model estimates the probability from data, and the only honest way to know whether its probabilities deserve trust is to grade them publicly over time: do the games it calls at 60% win about 60% of the time?
That is what calibration measures, and it is why every SharpDeck forecast is recorded before the game and graded after it, losses included.
Why +EV bets still lose
At 55%, a bet loses 45 times in 100. You can do everything right and lose five in a row; the math says that will happen regularly. Expected value describes an average that only emerges over hundreds of bets, and short stretches can look nothing like it.
Two practical consequences follow. First, stake sizes matter: an edge is worthless if a bad run forces you to stop. Second, judge a process by its long-run record, not by last night. Any betting results described in this guide are hypothetical illustrations; they are not a forecast of what you will earn.
How SharpDeck uses EV
Beside each forecast, SharpDeck shows the model probability, the best price across the sportsbooks it reads, the edge between them and the EV per dollar. Pro and Elite plans add a suggested stake size. EV is shown only when both a model probability and a fresh price exist — a missing input produces no number rather than a made-up one.
SharpDeck field notes. Product explanations and worked examples, not betting recommendations.