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How to Pick the Proper Bet Size

Publish Date: 03/27/2024

You found out about +EV betting, signed up to your first sportsbook and are about to place a bet. But how much should that bet be? $10, $25, or even $100? In this guide we'll briefly cover bankroll management and the tool we recommend you use to size your bet.

The Importance of Bankroll Management

Bankroll (noun); Your bankroll is the amount of money you are able to play with.

Your bankroll is your friend. Without it, there are no +EV bets, as there are no bets at all. Although everybody wants to be a whale bettor laying thousands of dollars on each game, that simply is not feasible for the vast majority of us.

Unit (noun); A specific measurement for betting, equal to 1% of your bankroll.

When digesting sports betting content, you will inevitably see the word unit as a way of measuring bet sizes, which equates to 1% of your bankroll strictly used for betting. Bettors like to use this word as a way of evening the playing field so that people with $100 in their bankroll can compare themselves to people with $100,000.

Although many people online want you to think otherwise, picking games above a 52.4% clip makes you profitable when betting against the spread, and many professional bettors will never eclipse 55% over the course of a season. Although a $10 bet when you have a $200 bankroll seems small, it is much better to be able to use your +EV skills for longer when the inevitability of negative variance goes against you, than to blow it all by making four $50 bets. There are going to be nights, and weeks, where you simply cannot win a bet, just like there are going to be hot streaks when you seemingly cannot lose. As your bankroll grows by winning +EV bets, so will your unit size.

Kelly Criterion

The way we at PromoGuy size our bets is using the Kelly Criterion. The purpose of the Kelly Criterion is to minimize your risk of losing your bankroll, while maximizing your potential profits. The formula will give you the optimal amount to bet given the money you have in your bank roll and the expected return on your investment.

The Kelly Criterion formula goes as such;

([Multiplier of your stake x probability of winning] - probability of losing) / multiplier of your stake) = Bet Size.

I know, that’s a complicated formula, so it is easier to see it in real betting terms. You want to bet the Bears as +200 underdogs against the Vikings. You believe that the Bears have a 40% chance of winning the game based on your +EV evaluations. The equation would look like: ([2 x .4] - .6) / 2 = .1. Understandably, not everybody likes to do algebra when placing a bet, so there are plenty of websites that will do the Kelly Criterion equation for you.

You will often see the Kelly Criterion broken down into divisors such as “Full, half, and quarter” Kelly. At PromoGuy we suggest using Quarter Kelly, or 1/4th of the optimal bet size in order to be a bit more conservative, and help us navigate the aforementioned negative variance. Sometimes it will be shortened to “QK” which of course means Quarter Kelly.

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