Sports betting fundamentals

Before we get any further, you need to understand how sportsbooks operate, how odds communicate information, and what different bet types mean. This article covers a couple of essential building blocks: reading American odds and converting odds into probability.

What happens when you place a bet

When you place a bet, you’re entering an agreement with a sportsbook. You risk a specified amount, and if your prediction is correct, the sportsbook pays you based on the odds. If you’re wrong, you lose your stake.

The sportsbook acts as an intermediary, taking bets from many customers on different outcomes of the same event. Sportsbooks make money by building a commission into the odds. This commission is called the vig (short for vigorish), and it’s how they guarantee profit over time regardless of which side wins.

American odds: Reading the numbers

American odds use positive and negative numbers to communicate two things: which side is favored, and how much you can win. Every odds line follows this format.

Negative odds (favorites)

A negative number like -150 or -200 indicates the favorite—the side more likely to win. The number tells you how much you must bet to win $100.

Examples:

-150: Bet $150 to win $100 (total return: $250)
-200: Bet $200 to win $100 (total return: $300)
-110: Bet $110 to win $100 (total return: $210)

The higher the negative number, the bigger the favorite and the less you profit relative to your stake.

To calculate your profit on any amount with negative odds:

\text{Profit} = \frac{\text{Stake} \times 100}{|\text{Odds}|}

Example: Betting $50 at -200 yields $\frac{50 \times 100}{200} = 25$ profit, for a total return of $75.

Positive odds (underdogs)

A positive number like +150 or +200 indicates the underdog—the side less likely to win. The number tells you how much profit you make on a $100 bet.

Examples:

+150: Bet $100 to win $150 profit (total payout: $250)
+200: Bet $100 to win $200 profit (total payout: $300)
+110: Bet $100 to win $110 profit (total payout: $210)

The higher the positive number, the bigger the underdog and the more you profit relative to your stake.

To calculate your profit on any amount with positive odds:

\text{Profit} = \frac{\text{Stake} \times \text{Odds}}{100}

Example: Betting $50 at +200 yields $\frac{50 \times 200}{100} = 100$ profit, for a total return of $150.

Even odds

Odds of +100 mean a $100 bet wins exactly $100—even money, representing a roughly 50-50 proposition.

Converting odds into probability

Every odds line contains the implied probability—the sportsbook’s estimate of how likely each outcome is. Converting odds to probability helps you understand what the numbers really mean.

Negative odds to probability

For negative American odds, use this formula:

\text{Probability (\%)} = \frac{|\text{Odds}|}{|\text{Odds}| + 100} \times 100

Example: -200 converts to:

\frac{200}{200 + 100} \times 100 = \frac{200}{300} \times 100 = 66.67\%

Example: -110 converts to:

\frac{110}{110 + 100} \times 100 = \frac{110}{210} \times 100 = 52.38\%

Positive odds to probability

For positive American odds, use this formula:

\text{Probability (\%)} = \frac{100}{\text{Odds} + 100} \times 100

Example: +200 converts to:

\frac{100}{200 + 100} \times 100 = \frac{100}{300} \times 100 = 33.33\%

Example: +150 converts to:

\frac{100}{150 + 100} \times 100 = \frac{100}{250} \times 100 = 40\%

These formulas let you quickly translate any odds line into a probability estimate. Keep in mind that implied probability includes the sportsbook’s margin (vig), so it’s slightly inflated compared to the true probability.

Reading a bet slip

When you place a bet, your betting slip shows:

Risk/Stake: The amount you’re wagering
To Win: The profit if your bet succeeds
Total Return/Payout: Your original stake plus your winnings

Example: A slip showing “Risk: $110, To Win: $100, Total Return: $210” at -110 odds means you must bet $110, and if you win, you receive $210 total ($110 stake returned plus $100 profit).

What is a push?

A push occurs when the final result lands exactly on the spread or total, creating a tie. When this happens, your stake is refunded—you neither win nor lose.

Example: You bet Steelers -3, and they win exactly 24-21 (3-point margin). The bet pushes, and you get your money back.

Using half-point lines (like -3.5 or 48.5) eliminates the possibility of a push.

Parlays

A parlay combines multiple individual bets into one wager where all selections must win for the bet to pay out. Parlays offer higher potential payouts because the odds of each leg multiply together, but a single loss forfeits the entire bet.

Example: A three-leg parlay combining Chiefs moneyline -150, Steelers -3, and Over 48.5 requires all three outcomes to be correct. If two win but one loses, the entire parlay loses.

If one leg results in a push, that leg is removed and the parlay continues with the remaining selections at adjusted odds. If all legs push, the entire parlay is refunded.

Parlays are attractive to recreational bettors because of large payouts, but they carry significantly more risk than individual bets. The vig compounds with each leg, making them less favorable than they appear. More on this in other articles.

Mastering American odds and converting odds into probability gives you the foundation to become a successful sports bettor. From here, you can begin learning how to evaluate bets, manage your bankroll, and identify value.