Key takeaways

• An arb appears when two books price the same outcome differently enough that the best prices add up to less than 100% implied probability.

• The manual method is a price comparison: the same market at several sportsbooks and prediction markets, the best price on each side, then the 100% test.

• Including a no-vig prediction market such as Novig on the screen lowers the total on one side, which makes the 100% line easier to clear.

• A scanner is worth paying for when your monthly volume covers its cost. At a 1.5% average return, a $100-a-month tool needs about $6,667 in monthly arb stakes to break even.

Where arbs come from

Every sportsbook sets and moves its own prices. FanDuel, DraftKings, BetMGM and Caesars react to news and to the money they take at different speeds, so for a few minutes after a line moves at one book, another can still be offering the old price. Prediction markets add another source of disagreement, because their prices come from orders placed by traders rather than a trading desk.

An arb is that gap caught while it's open. Finding one is mostly a matter of looking at enough prices for the same market, quickly enough, to see when the best price on each side comes from a different book.

The manual workflow

1. Pick one market. Start with a single game and a single bet type, such as an NBA moneyline or an NFL total.

2. Open the same market everywhere you have an account. That means the sportsbooks available in your state, plus prediction markets such as Novig, Kalshi or Polymarket US where they operate.

3. Record the best price on each side. Note which book or platform it came from.

4. Convert and add. Turn both prices into implied probability and add them up. The arbitrage calculator does this as you type.

5. Check the details if the total is under 100%. Add any prediction market fee to the price, confirm the order book has enough depth, and make sure both legs settle under the same rules.

6. Place both legs. Put the leg most likely to move first, and confirm both before treating the profit as locked.

The arbitrage math guide covers step 4 in detail, and the common mistakes guide covers what goes wrong in steps 5 and 6.

Where prices tend to disagree

Some markets give prices more room to drift apart:

• Markets that move on news: right after an injury report or a lineup change, books update at different speeds.

• Player props and alternate lines: books price far more of these than main lines, and each book weights them differently.

• Less popular leagues and games: lower betting volume means prices get corrected less often.

• Two-sided markets with a no-vig price available: a sportsbook price that's only slightly generous can still produce an arb against a prediction market price that has no vig built in.

The last point is where a prediction market earns its place on a price screen. Two sportsbooks each carrying a -110/-110 hold need to disagree by more than 4.76% before an arb appears. A no-vig price on one side removes most of that gap, which is how a FanDuel price at -105 can produce a 1.78% arb against a 47¢ contract on Novig's pre-game market. The prediction market guide works through that example with each platform's fees.

When a scanner pays for itself

Checking prices by hand works for a few markets at a time. Arb scanners such as OddsJam, RebelBetting and BetBurger check prices across many books continuously and flag the gaps, which is hard to match by hand once you're watching more than a few markets. They charge a subscription.

Whether one is worth it comes down to volume. Divide the monthly cost by your average return per arb to get the monthly stake needed to break even:

Below those numbers, the manual method and a free calculator make more sense. Above them, the time a scanner saves is the main reason to pay.

Whatever finds the arb, the checks in step 5 still apply. A scanner can flag a price that has already moved, a market with thin depth, or two legs with different settlement rules.

Finding arbs questions

How long do arbs last?

It varies by market. A gap on a popular game can close within minutes once the slower book updates, while a gap on a less popular market can last longer. The safe assumption is that the price you see is about to change.

How many sportsbook accounts do I need?

More accounts mean more prices to compare, which means more arbs. The limit is how many books are licensed in your state and how many prediction markets operate there.

Do I need a scanner to start?

No. Comparing a few markets by hand and running the prices through a calculator is a reasonable way to learn how arbs behave before paying for software.

Will finding arbs get my sportsbook accounts limited?

Placing them can. The account limits guide covers what sportsbooks look for and what Massachusetts found when it reviewed the practice.

Check the prices you found

Enter the best price on each side in the arbitrage calculator to see whether it's an arb and how to split the stake.