How alerts work · Plus Side

What an arbitrage is

Every price a sportsbook offers implies a probability. A book that offers the Bears at +145 is saying they win about 41% of the time. Each book also builds in its own margin, so one book's prices for both sides of a game add up to more than 100%.

Different books don't always agree, though. When the best price on each side comes from a different book, the two can add up to less than 100%. Bet both sides at the right stakes and you get back more than you put in, whichever team wins.

	Bears at FanDuel	Lions at BetMGM
American odds	+145	−130
Decimal odds	2.4500	1.7692
Implied probability	40.82%	56.52%
Both sides together	97.34%

The total is 2.66 points under 100%. That gap is the edge. As a return on everything you stake, it works out to 100 ÷ 97.34 − 1 = 2.73%, which is the margin the alert shows.

Converting odds

Alerts show American odds, since that's what US books display. To do the math yourself, convert to decimal odds first. A decimal price is what a $1 bet returns, stake included.

Positive odds:  decimal = 1 + odds ÷ 100        +145 → 2.45
Negative odds:  decimal = 1 + 100 ÷ |odds|      −130 → 1.7692
Implied probability = 1 ÷ decimal               2.45 → 40.82%

Sizing the stakes

Each bet's share of the total is its implied probability divided by the total of both. That split makes every outcome pay the same.

Bears stake = $100 × 40.82 ÷ 97.34 = $41.93
Lions stake = $100 × 56.52 ÷ 97.34 = $58.07

Bears win:  $41.93 × 2.45   = $102.73
Lions win:  $58.07 × 1.7692 = $102.74

Every alert is sized on a $100 total, rounded to the cent. To bet $250 instead, multiply both stakes by 2.5. Rounding can shave a cent or two off the return, but the margin is rechecked after rounding.

Placing both bets

Check the quote age. Prices can be up to 2 minutes old when the alert posts. If an alert is older than that, check both prices at the books before you start.
Place the bet most likely to move first. That's usually the price furthest from what other books offer, since it's the one most likely to be corrected.
Place the second bet right away. Before you confirm it, compare its price with its break-even price in the alert.
Note what you placed. Track your stakes, prices and results somewhere, even a spreadsheet, so you know your real return.

When a price moves

The break-even price is the worst price a bet can move to before the margin hits zero. In the example, with the Bears bet placed at +145, the Lions bet still breaks even at −145. Anywhere from −130 to −145, you still make a profit, just a smaller one.

If the second price has moved past break-even, you have three choices:

Find it elsewhere. Another book may still offer the Lions at −145 or better.
Hedge for a small loss. At −150, a Lions stake of $61.64 brings back $102.73 either way on $103.57 staked, a loss of $0.84. That's often better than leaving $41.93 riding on one result.
Keep the single bet. It's now an ordinary bet that can win or lose. Only do this with money you're comfortable losing.

If a bet is rejectedBooks sometimes refuse a bet or cut its size. Treat it like a price move: check the break-even price, then find the other side elsewhere or hedge.

Three-way markets

Soccer moneylines have three outcomes: home, away and draw. A three-way alert has three bets, often at three different books. The math is the same. The three implied probabilities must add up to less than 100%, and each stake is that outcome's share of the total.

+EV alerts

A +EV alert is a single bet whose price is better than the fair price. To find the fair price, Plus Side takes prices from sharp books, which take big bets and move their lines quickly, and removes their margin.

Say a sharp book offers both sides of a game at −110. Each implies 52.38%, 104.76% together. Removing the margin leaves 50% each, a fair price of +100. If another book offers +105, a $100 bet returns $205 half the time, which is worth $102.50 on average. That's a 2.5% edge.

The difference from arbitrageA +EV bet wins or loses outright. The edge only shows up over many bets, so expect losing streaks and size each bet so you can ride them out.

What can go wrong

Prices move. Lines can change between your first and second bet. The break-even price tells you how much room you have.
Books limit winning accounts. Sportsbooks can cut the stakes of accounts that win or bet both sides. It's the most common reason arbitrage bettors stop.
Rules differ. Books can settle the same game differently after overtime, a postponement or a player scratch. They can also void bets on an obvious pricing error. Check both books' rules before you bet.
Quotes can be stale. Prices come from an odds data provider that refreshes about once a minute. Always confirm the price at the book.

Glossary

American odds: The US price format. +145 means a $100 bet wins $145. −130 means you bet $130 to win $100.
Decimal odds: What a $1 bet returns, stake included. +145 is 2.45.
Implied probability: The chance a price implies: 1 divided by the decimal odds.
Margin: Your profit as a share of the total stake, whichever side wins.
Break-even price: The worst price a bet can move to before the margin hits zero.
Leg: One bet in an arbitrage. A two-way arbitrage has two legs.
Vig or hold: The margin a sportsbook builds into its prices, so both sides add up to more than 100%.
Fair price: A price with the vig removed, taken from sharp books.
+EV: Positive expected value: a price better than the fair price, so it's worth more than it costs on average.
Quote age: How old a price was when the alert posted.

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