Selecting Profitable Bets and Calculating Bet Size

In sports betting, there is an inherent disadvantage to the bettor.  The sportsbook charges a small amount of commission on each bet, which is passed onto the customer in the form of “vig” or “juice”.  

For example: Team A and Team B both have a 50% chance of winning a game. If betting were a fair endeavor, the sportsbook would pay even money (+100) for a winning bet on either team.  However, in the United States, you often see a 50/50 game with odds of -110.  This means that instead of winning even money on this bet, the sportsbook charges a 10% markup. This is how they make their money, and it’s what we aim to avoid by betting strictly odds boosts, promotion bets, and other +EV situations!

Our Process 

The first step to using promos and odds boosts to build a bankroll is to be able to determine how much to bet on a given game.  Here’s a step-by-step process of how I find a potential play and figure out the ideal bet size, with an example from July 13, 2021 to demonstrate. 

Step 1: Identify potentially profitable bet

Step 2: Find true probability of the bet hitting

Step 3: Use true probability and the Kelly Criterion to determine optimal bet sizing

Let’s break down each step of the process individually:

Step 1: Identify potentially profitable bet 

Some odds boosts and promos are good - others are not.  Instead of testing each and every boost with this method, I usually look for a few things:

  • Gut feeling: Does the boost seem to be worthwhile at first glance? If not, I usually don’t bother calculating anything.
  • Hard numbers: How big is the “boost”? Books often attach a meaningless number on the non-boosted price of a bet.  Use a consensus odds site (Pinnacle Sports is the gold standard here, with OddsJam being the best way to access this info) to see if the original number is reasonable.
  • Interest: unless it looks like a slam dunk no-brainer, I usually only bet on games I’m somewhat interested in. This is just a personal preference.
Step 2: Find true probability of the bet cashing 

Like I said before, sportsbooks charge “juice” or “vig” on each bet in order to make a profit.  It’s in our best interest to find out exactly how much vig they are charging in order to learn the true probability of each outcome. I use the no-vig calculator on this site (note on OddsJam at the end). Use Pinnacle’s odds to calculate this - they’re the best book out there.

Step 3: Use true probability (from Step 2) and the Kelly Criterion to determine optimal bet size

Once we know how likely it is for a bet to cash, we need to know how much to bet on it.  Most promos are capped at $50, but it’s still useful to go through this process.  For more info on the Kelly Criterion, here’s a link. 

Using THIS site, now we plug in our numbers (Probability, Odds, Bankroll, and Adjusted Kelly).  “Probability” is a decimal between 0 and 1, “Odds” is basically the moneyline odds of the bet, “Bankroll” used for these calculations is $1000, and “Adjusted Kelly” is always going to be 1.

Let’s do an example in order to demonstrate the process. The following is what I go through for every bet that is posted on Twitter. Instead of doing all of that yourself, we’ll do it for you! Follow along here: 

Twitter: @PromoGuyMI 

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EXAMPLE: July 13, 2021

Caesars (MI) has the AL to win the All Star Game boosted to +150 odds.


Step 1: Identify potentially profitable bet 

  • Gut feeling: Right off the bat, most all star games are a toss-up. +150 looks like a good number for a toss-up. Let’s move on
  • Hard numbers: Pinnacle Sports has the following odds: NL -114, AL +106
  • Interest: I’ll be watching anyway. Let’s do this.

Step 2: Find true probability of the bet winning

Going back to our “no vig” calculator, we plug in “106” and “-114” to see the actual odds for tonight’s game. We come up with the following numbers:

Since the AL is +106 to win, we see that based on a consensus of market odds, this bet is 47.68% likely to cash. Let’s move on to the final step (continued on next page).

Step 3: Use true probability (from Step 2) and the Kelly Criterion to determine optimal bet size

Moving over to the Kelly Criterion calculator, we plug in our true probability and other numbers. Since the bet is boosted to +150, our “odds” section needs to read “1.5”. Here’s what we get:

At the bottom, it says “Bet This Much”. The optimal bet sizing for the American League +150 to win tonight’s All Star Game is $128.  Since we’re capped at $25 by Caesars, we max it out. 

The American League DID win this game, so we won our bet!


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