How to Compare Odds and Shop for Lines
Different sportsbooks post different prices on the same game. This article shows with worked examples how to compare moneylines, totals and run lines, what the margin is, and why a better price lowers cost without guaranteeing profit.
The same baseball game is rarely priced the same way at two sportsbooks. One book may list the home team at -150, another at -140, a third at -145, and the gap looks too small to care about until you work out what it means in dollars and in probability. Comparing prices before you place a bet, known as line shopping, is a basic habit of careful bettors, and it is the one part of the activity where arithmetic is on your side.
It is also the most misunderstood. Shopping for a better price does not make a bet a good one, and it does not guarantee a profit. What it does is reduce the cost of a wager you were already going to make. This article explains how to compare prices in the three common baseball markets, how to see the margin built into any price, what a few points of difference are worth, and where the limits are. It contains no picks and no advice about which team to back.
Betting on baseball carries risk, and most people who bet lose money over time. Sports betting is for adults of legal age where it is legal, and legality, age limits and licensing rules vary by state and country. If gambling is causing problems, call 1-800-GAMBLER in the United States, or visit the National Council on Problem Gambling. The article on responsible gambling and baseball covers limits and warning signs in detail.
Why prices differ at all
A sportsbook sets its prices by estimating the probability of each outcome and then adding a margin so that it earns money whichever side wins. Every book has its own estimate, its own customers and its own views on risk. If a book takes more money on one side than it wants, it may move the price to attract bets on the other. Another book may not have taken the same action and leaves its price where it was. The result is a spread of prices for the same game at the same moment.
That spread is the reason shopping works. The difference between two books is usually small, a few cents on a moneyline, half a run on a total, or a few points of price on a run line. It is a difference nonetheless, and over many bets it is the largest controllable factor in what betting costs.
A word on terms. A price or line is the odds on a bet. The moneyline is a bet on who wins, with no points involved. A run line is baseball's version of a point spread, most often 1.5 runs. A total, or over/under, is a bet on whether the combined runs by both teams will be above or below a number. The article on season win totals covers the long-season version of the same idea.
Converting prices so they can be compared
American odds, the style used in the United States, show a favorite with a minus sign and an underdog with a plus sign. To compare prices, it helps to translate them into two numbers: the profit on a standard stake and the implied probability.
For a favorite at -150, you risk $150 to win $100, so a $100 stake wins $66.67. The implied probability is 150 divided by 250, or 60.00 percent. For a favorite at -140, a $100 stake wins $71.43 and the implied probability is 140 divided by 240, or 58.33 percent. For an underdog at +130, a $100 stake wins $130 and the implied probability is 100 divided by 230, or 43.48 percent. At +120 the stake wins $120 and the probability is 45.45 percent.
| Price | Profit on $100 | Decimal odds | Implied probability |
|---|---|---|---|
| -150 | $66.67 | 1.667 | 60.00% |
| -140 | $71.43 | 1.714 | 58.33% |
| -110 | $90.91 | 1.909 | 52.38% |
| -105 | $95.24 | 1.952 | 51.22% |
| +120 | $120.00 | 2.200 | 45.45% |
| +130 | $130.00 | 2.300 | 43.48% |
Decimal odds, shown in the third column, are the easiest way to compare quickly: a higher decimal number is always a better price for the bettor, regardless of whether the American price is positive or negative. The article on converting baseball betting odds to implied probability walks through the formulas.
A moneyline example
Suppose two books post the same game. Book A has Team X at -150 and Team Y at +130. Book B has Team X at -140 and Team Y at +120. These are invented numbers for illustration, not a real game.
Add the implied probabilities at each book. At Book A, 60.00 plus 43.48 is 103.48 percent. At Book B, 58.33 plus 45.45 is 103.79 percent. Both numbers exceed 100 percent, and the excess is the book's margin, sometimes called the vig or juice. A market with no margin would add to exactly 100. Book A takes about 3.5 points of margin on this game, and Book B about 3.8.
Now notice something. Book B is better for a bettor who likes Team X, because -140 pays more than -150. Book A is better for a bettor who likes Team Y, because +130 pays more than +120. Neither book is the better one overall. If you could take Team X at Book B and Team Y at Book A, the best prices would add to 58.33 plus 43.48, or 101.81 percent, which is a smaller margin than either book offers alone. That is the idea of line shopping in one line: the best available price on each side is better than any single book's pair.
Of course, a bettor takes only one side, so the practical lesson is simpler. Whichever side you choose, check every book you can legally use and take the best price. A book with the lowest overall margin is not always the book with the best price on your side.
What a few points of price are worth
A small price difference sounds trivial. Here is a way to see the size of it. Assume, purely for illustration, that you believed Team X wins 58 percent of the time. At -150, a $100 bet has an expected result of 0.58 times $66.67 minus 0.42 times $100, which is about negative $3.33. At -140, the same bet has an expected result of 0.58 times $71.43 minus 0.42 times $100, which is about negative $0.57. The difference between the two prices is roughly $2.76 per $100 staked.
Look at what that example does and does not show. It shows that the better price costs less on average, and that over hundreds of bets the saving adds up. It also shows that both bets have a negative expected result if your estimate is 58 percent, because the break-even probability at -140 is 58.33 percent. Shopping lowered the cost of a losing proposition. It did not turn it into a winning one. A price is only good if your estimate of the probability is better than the price implies, and estimating baseball games better than the market is hard. Favorites lose often even when the estimate is right, a point covered in why baseball favorites lose so often.
This is why the honest framing of line shopping is cost control. If you are going to bet, the lower-cost price is better than the higher-cost one. That is not the same as a reason to bet.
Totals and run lines
Totals look simple, but the same shopping logic applies in more than one way. A total of 8.5 runs at -110 on both sides implies 52.38 percent on each side, 104.76 percent in all, so the margin is about 4.76 points. A book offering the same total at -105 on both sides implies 51.22 percent on each side, 102.44 percent in all, a margin of about 2.44 points. The same bet is cheaper at the second book.
The number itself matters too. A total of 8.5 cannot be tied. A total of 9 can land exactly on 9 runs, and when it does, the bets are returned as pushes. A book that offers 9 at -110 and a book that offers 8.5 at -110 are not offering the same bet, because the first has a chance of refunding stakes and the second does not. Comparing a half-run difference is therefore part of shopping, but it is harder to price than a cents difference, and bettors who compare must be careful to compare like with like.
Run lines work similarly. The standard run line gives the favorite -1.5 runs and the underdog +1.5. As an invented example, an underdog at +1.5 might cost -160 at one book and -150 at another, and a favorite at -1.5 might pay +150 at one book and +160 at another. At +150 the implied probability is 40.00 percent and at +160 it is 38.46 percent. Because a baseball favorite must win by two or more to cover, the run-line prices are far from the moneyline prices, and the shopping logic applies independently to each market.
Another baseball-specific term is the listed pitcher. Many books price a game assuming certain starting pitchers and will cancel or reprice a bet if a starter is scratched. Some books offer an "action" option that keeps the bet live whoever pitches. The rules differ from one book to the next, so read the terms before placing a bet, because a better price with the wrong pitcher condition is not a better price.
Lines move
A line is a snapshot. Prices change as new information arrives: a starter is confirmed, a lineup is posted, the weather forecast changes, an injury is reported, or the book gets too much money on one side. A price you see in the morning may not exist by the afternoon. The first price a book posts is called the opening line, and the last one before the game starts is the closing line.
Experienced bettors often use the closing line as a benchmark. If you routinely take prices that are better than the closing price, you may be seeing something the market has not yet absorbed. If you routinely take prices that are worse, the market is moving away from your side. That is a way of judging a bettor's process that does not depend on a single game's outcome. It is not a guarantee of anything, and the closing line is an estimate that the market has been wrong about plenty of times.
The practical point for shopping is that comparisons expire. Check prices at the moment you are ready to bet, and be skeptical of any comparison table, including one on this site's odds pages, as a record of the past rather than a promise of the present.
Parlays and the margin that compounds
A parlay combines two or more bets into one, and it pays only if all of them win. Parlays are popular because the payout is large. They also compound the margin. Take two bets at -110 each. A single bet at -110 has an implied probability of 52.38 percent, which exceeds the 50 percent a fair coin flip would warrant by 2.38 points. Two such bets in a parlay pay about +264, the product of two decimal prices of 1.909, which is 3.645. A fair price for two independent 50 percent events would be 4.0, or +300. The parlay's implied probability is about 27.4 percent, against 25 percent for the true event, so the margin on the parlay is roughly 9.8 percent in relative terms, about double what each leg carries.
The more legs, the more the margin compounds. That does not mean parlays are wrong for everyone, but it does mean that if you are shopping for price, the cost of a parlay is higher than the cost of the legs separately. Same-game parlays, which combine outcomes within one game, add another layer because the outcomes are connected, which makes the pricing harder to judge.
The sure-bet myth
Sometimes the prices at two books differ so much that a bettor could bet both sides and lock in a profit regardless of who wins. This is called arbitrage, and it can exist briefly. Suppose Book A offers Team X at +110 and Book B offers Team Y at +105. The decimal prices are 2.10 and 2.05. The implied probabilities, 47.62 percent plus 48.78 percent, add to 96.40 percent, less than 100. If you stake about $49.40 on Team X at Book A and about $50.60 on Team Y at Book B, either result returns about $103.73, a profit of roughly $3.73 on $100 of total stake.
In practice, such opportunities are rare and disappear in minutes. Prices move while you place the second bet, books can cancel bets placed at a clearly mistaken price, and books may limit or close accounts that they believe are being used only to chase price gaps. The arithmetic is real. The ease is not. Anyone who sells a method as a guaranteed profit is selling something other than a guarantee, and there is no betting approach that removes risk.
Practical habits
Use only licensed, regulated sportsbooks in places where betting is legal, and confirm that you meet the age requirement in your jurisdiction. Keep a record of your bets, with the price, the book and the result, so you can see what betting costs you over time instead of relying on memory. Decide in advance how much you can afford to lose and stick to it, and do not use the idea of a better price as a reason to bet more than you planned. Winnings may be taxable, and a tax professional can explain the rules where you live.
Finally, remember the history behind the numbers. Baseball and gambling have been tied together for as long as the sport has existed, and the story of that relationship, including the scandals that shaped the rules, is told in the history of baseball and gambling. For the postseason, where prices are set differently, see betting on the postseason.
Common questions
What is line shopping? Comparing prices on the same bet across several sportsbooks and taking the best one. It lowers the cost of a bet but does not make a bet more likely to win.
What is the vig? The margin built into a price. You find it by adding the implied probabilities of every outcome in a market. If they add to more than 100 percent, the excess is the book's margin.
Is the best price always at the book with the lowest margin? No. A book with the lowest overall margin may still offer a worse price on the specific side you want.
Do I need accounts at several books? To shop you do, and each must be a licensed book in a place where you may legally bet. Remember that more accounts can make it easier to bet more than you planned.
Can I guarantee a profit by shopping? No. Shopping reduces cost; it does not remove the risk of loss.
Where to go next
If you want to practice the arithmetic, start with converting baseball betting odds to implied probability and then read why baseball favorites lose so often. The site's betting topic page collects current reading, and the odds pages show prices for reference. If betting has stopped being fun, call 1-800-GAMBLER or read responsible gambling and baseball.