Sports Betting for Beginners: How to Read the Odds Before You Risk a Dollar

By · author of the MIT-licensed teachersbettextbook library ·

One number on the board. Four ways to say it. Not one of them tells you who wins.

Meet your classmates

You will see these five all course. Here they are on day one.

Brian writes one number

Bookie Brian is not telling you who wins. He never guesses that. He is telling you what he will pay you, and what he wants from you first.

Today he is pricing a race between Chalk and Pip. He puts Chalk up at −145. One number. Everything else on this page comes out of it.

The same number, four costumes

−145 is how a board writes it. The minus means you risk more than you win.

As a ticket, it is risk $145 to win $100. Same number, in plain English.

As a percentage, it is 59.2%. That is how often the bet has to land just to break even. Still the same number.

In decimal odds it is 1.69. Every $1 comes back as $1.69 when it wins, your stake included. Same number, fourth outfit.

Then he prices the other side

Pip goes up at +125. Plus means you win more than you risk. Put up $100 and you win $125 on top of it, so $225 comes back.

As a percentage that is 44.4%. Now add the two sides together. 59.2 plus 44.4 is 103.6.

Reality does not do that. One race, two hamsters, exactly one of them wins. Honest probabilities have to come to 100.

And no, Chalk is not really a 59.2% hamster. She wins about half the time, same as Pip. The board never claimed otherwise, and the gap between those two things is lesson 2.

CHALK TO WIN AMERICAN ODDS−145the way a board writes it WHAT THE TICKET DOES$145 to win $100risk on the left, profit on the right IMPLIED PROBABILITY59.2%how often it has to win to break even DECIMAL ODDS1.69$1 comes back as $1.69, stake included AMERICAN THE TICKET PERCENT DECIMAL Average Joe Bookie Brian +EV Evan −145is that good? 59.2%is what it needs Both sides of the same race, as percentages CHALK −145 = 59.2% PIP +125 = 44.4% 100% 3.6 points Brian’s cut 59.2 + 44.4 = 103.6 One number on the board. Joe just stares at it. It says what to risk, and what comes back. It says how often it has to win. Evan reads this one. Four costumes, one number, and not one of them picks a winner.
One price, drawn four ways, and every number here is arithmetic you can redo. −145 means $145 risked for $100 of profit, so it needs 145 ÷ 245 = 59.2% to break even, and $1 comes back as 1 + 100/145 = $1.69. Pip’s +125 is 100 ÷ 225 = 44.4%. The two run to 103.6, and the 3.6 points past the dashed line are the vig. This one is a diagram rather than a simulation: nothing here is random, so nothing here can come out differently.

The extra 3.6 points are Brian's cut. The word for it is vig, and you pay it whichever hamster you back.

Which is why you are not really hunting for winners. You are hunting for prices that are wrong. That is lucky, because guessing winners is hard and reading a number is not.

The standard price on most markets is −110 on both sides. That one needs 52.4% to break even, on something built to be a coin flip. Two and a bit points, every single bet, forever.

Try it on any number

Type a price and a stake. It works out the profit, the total back, the percentage, and the record you would need, and it shows the arithmetic while it does it.

That percentage still has Brian's cut inside it. It is what the price charges, not what the hamster is worth. Taking the cut out is the de-vig lesson.

Three habits, starting today

And the oldest rule. The moment this stops being arithmetic and starts being a chase, stop. If it ever feels like that, 1-800-GAMBLER is free and staffed around the clock.

Want more math?the Nerd Corner

Nerd Corner

Advanced material. Nothing above depends on it.

Every step, on one price

Raw number to the fee inside it, six steps. This is exactly what the app runs on live prices.

The same $25 on each side

Worked example: two $25 tickets

On the favorite at −145:b=100145=0.6897,profit=$25×0.6897=$17.24\text{On the favorite at } -145:\quad b = \tfrac{100}{145} = 0.6897,\quad \text{profit} = \$25 \times 0.6897 = \$17.24
Ticket if it wins: $25+$17.24=$42.24 back\text{Ticket if it wins: } \$25 + \$17.24 = \$42.24 \text{ back}
On the underdog at +125:b=125100=1.25,profit=$25×1.25=$31.25\text{On the underdog at } +125:\quad b = \tfrac{125}{100} = 1.25,\quad \text{profit} = \$25 \times 1.25 = \$31.25
Ticket if it wins: $25+$31.25=$56.25 back\text{Ticket if it wins: } \$25 + \$31.25 = \$56.25 \text{ back}
Same $25, different payouts. The book charges more to back the likelier team, and a losing ticket pays $0 either way.

Spreads and totals, in one paragraph

A point spread handicaps the favorite: Cowboys −6.5-6.5 must win by 7 or more. A total asks whether the combined score goes over or under a posted number. Both are built to be near coin flips, so both sides usually sit near −110-110. Same math: two outcomes, two prices, implied probabilities overshooting 100% by the fee.

What the cut adds up to

Nobody feels 4.5 cents. Everybody feels what it turns into:

Worked example: 100 flat bets at −110

One bet: $25 at −110 on a true 50/50:EV=0.5×$22.73−0.5×$25=−$1.14\text{One bet: } \$25 \text{ at } -110 \text{ on a true 50/50}:\quad \mathrm{EV} = 0.5 \times \$22.73 - 0.5 \times \$25 = -\$1.14
One hundred bets: 100×(−$1.14)≈−$114\text{One hundred bets: } 100 \times (-\$1.14) \approx -\$114
Win exactly half (a fair record) and the standard price still costs about $114 per hundred $25 bets. That’s the rent the fee collects.

Keep score from day one

Three free habits:

Where these conventions come from

Nearly everything above is arithmetic you can re-run. The one documented fact: books charge eleven-for-ten and collect the vig as commission.[1] The reading on fee-removal methods lives in the de-vig lesson.

  1. Levitt, S. D. (2004). “Why are Gambling Markets Organised so Differently from Financial Markets?” The Economic Journal 114(495), 223–246. Source for the standard “pay $110 on a loss, collect $100 on a win” price, the vig as the book’s commission, and the 52.4% break-even it forces.

Check your understanding

Frequently asked questions

What does −110 mean in sports betting?

Minus odds state what you must risk to win $100, so −110 means risk $110 to win $100 of profit. It implies a 52.4% win probability (110 ÷ 210), and it is the standard price on point spreads and totals.

How do you convert American odds to implied probability?

For minus odds, divide the number by itself plus 100: −145 implies 145 ÷ 245 = 59.2%. For plus odds, divide 100 by the number plus 100: +125 implies 100 ÷ 225 = 44.4%. The result still contains the book’s fee.

What is the vig (juice) in sports betting?

Add up the implied probabilities of both sides of a game and they exceed 100%: a standard −110/−110 pair sums to 104.8%. Real probabilities must sum to exactly 100%, so the overshoot is the book’s built-in fee, charged on every bet whether you notice it or not.

Do I need to place a bet to use these lessons?

No. Teacher’s Bet is an analytics tool, not a sportsbook: it takes no wagers and gives no picks. Every lesson and calculator is free and works on numbers you type in. You can learn the entire course without risking a cent.