Learn the Math Behind the Bet
Evergreen explanations of the arithmetic behind sportsbook prices. No systems, no picks, no promises — just the math.
What Is Expected Value in Sports Betting?
Expected value — EV — is the average amount a bet would win or lose per dollar staked if you could place the same bet many times. It compares the price you are offered to the estimated fair probability of the outcome.
Read the guide →What Is Sportsbook Vig?
The vig — short for vigorish, also called juice or margin — is the fee a sportsbook builds into its prices. It is why both sides of a coin-flip market are usually -110 instead of +100.
Read the guide →Fair Odds vs Sportsbook Odds
The price a sportsbook offers is not a pure statement of probability — it includes the book's margin. Estimated fair odds are what the price would look like with that margin removed.
Read the guide →Why Parlays Have More Vig
Every leg of a parlay carries the sportsbook's margin. Because parlay payouts multiply, the margins multiply too — so the total margin on a parlay is far larger than on any single bet.
Read the guide →How Parlay Probability Works
A parlay only wins if every leg wins. Under the assumption that the legs are independent, the combined probability is the product of each leg's probability.
Read the guide →What Is Bet Correlation?
Two bets are correlated when the outcome of one changes the likely outcome of the other. Standard parlay math assumes legs are independent; correlation breaks that assumption.
Read the guide →Why Same-Game Parlays Are Different
A same-game parlay combines legs from a single game. Because those outcomes influence each other, the standard multiply-the-probabilities math no longer applies cleanly.
Read the guide →Why Positive EV Does Not Mean Guaranteed Profit
Positive expected value means the price is favorable relative to the estimated fair probability. It is a statement about averages over many bets — never about the outcome of any single one.
Read the guide →Prefer to run the numbers?
Every guide links to a free calculator, and the methodology page documents exactly how EVScout computes estimates. When you're ready, evaluate a parlay and see the math applied to your own ticket.