Expected value · NetArbs guide
What makes a bet positive expected value?
Expected value (EV) is the average profit or loss a wager would have over many repeats at the same true probability and price. A positive estimate is only as credible as the probability used to calculate it.
Price and probability are different inputs
The offered odds determine your payout and break-even point. A fair probability comes from an independent estimate, such as a no-vig consensus of comparable sportsbook lines. Using the same offered price as both your probability and payout does not establish an edge.
A price can move while a quote is being collected. Recheck the line, player, stat, side and limit at the book before placing a wager.
Why several books matter
One sportsbook can be stale or simply disagree with the market. A consensus built from enough independent, matching quotes is more useful than a single reference price. If those quotes disagree sharply, confidence in a precise EV number should fall.
NetArbs shows the number of contributing books and filters out unsupported or implausibly large differences. That reduces noise, but it cannot certify the true probability of an event.
Track decisions, not just wins
Short-term results are noisy. Record the odds available when a choice was made and compare them with later market prices. Closing-line value can help assess whether a process consistently found favorable prices, but it does not guarantee profit on any individual bet.
Use a stake you can afford to lose. An EV estimate does not remove outcome risk.
See the method in NetArbs
Use the live tool to inspect the current prices and their sources. Quotes and payouts can change after this example was written.