Plus and Minus Odds: Why +150 and -150 Aren’t Opposites

Plus and minus odds are not mirror images of each other. A +150 price and a -150 price use the same digits and opposite signs, but they describe different risks and different rewards: +150 pays $150 profit on a $100 stake, while -150 pays only $66.67 profit on a $100 stake. In probability terms, +150 implies 40% and -150 implies 60%. The two numbers are complements, not equals. This matters because the plus and minus signs invite a symmetry that the underlying math does not have. Most of the confusion about how to read American odds comes from treating the scale as if the distance above even money matched the distance below it. It does not, and there is even a gap in the middle of the scale where no price can exist. This article shows the exact formulas, works through a side-by-side example with hypothetical prices, explains what the -100 to +100 gap means, and shows how to compare two prices at equal risk. All example odds are illustrations, not current sportsbook lines.

Why +150 and -150 Are Not Mirror Images

A mirror image would mean that +150 is to an underdog what -150 is to a favorite, in every respect. In one respect it nearly is: the implied probabilities add up to 100%. A +150 price implies a 40% chance, a -150 price implies a 60% chance, and 40% plus 60% is 100%. A market that listed exactly those two prices on opposite sides of one game would carry no sportsbook margin at all.

In every other respect the two prices differ. The same $100 stake behaves differently: at +150 it profits $150 if it wins, and at -150 it profits $66.67. The break-even point differs too, since a bettor needs to win more than 40% of +150 bets to come out ahead, and more than 60% of -150 bets. A deeper treatment of that threshold sits in the article on implied probability in sports betting.

The sign tells you which side is the favorite or underdog, and the number tells you the price relative to a $100 benchmark. The two signs use different benchmarks. A positive number states how much profit a $100 stake earns. A negative number states how much must be risked to earn $100 of profit. Because the benchmark changes depending on the sign, the two halves of the scale are measuring different things, which is the root of the asymmetry.

How the Formulas Work and Why the Scale Bends

Each sign has its own formula. For an underdog, implied probability is 100 divided by the odds plus 100. For a favorite, it is the absolute value of the odds divided by the absolute value plus 100. Two different formulas are needed because the benchmark flips between them. The formulas are not just arithmetic. Each one returns the break-even win rate for that price, the share of bets that must win before the price stops costing you money.

For payouts the logic is similar. At positive odds, profit equals the stake times the odds divided by 100. At negative odds, profit equals the stake times 100 divided by the absolute value of the odds. In both cases the payout is the stake plus the profit, so payout always includes the stake while profit never does.

The dead zone between -100 and +100

Plot the American scale and you will notice that no price is ever quoted between -100 and +100. A price of +50 or -50 does not exist. This is because both -100 and +100 mean even money: risk $100 to win $100, an implied probability of 50%. The scale does not run continuously through zero. It starts at even money, then runs outward in two directions, upward through +101, +102 and beyond for underdogs, and downward through -101, -102 and beyond for favorites.

The 200-point gap on the number line is therefore not a real gap in probability. Moving from -110 to +100 lowers implied probability by only 2.38 points, from 52.38% to 50%. Equal changes in the number mean unequal changes in probability. A 10-point move from +500 to +510 shifts implied probability from 16.67% to 16.39%, a change of about 0.27 percentage points. A 10-point move from -110 to -120 shifts it from 52.38% to 54.55%, a change of about 2.16 points. The same 10 points carry roughly eight times more weight near even money than far out on the underdog side.

Worked Example: +150 Against -150

Suppose a sportsbook lists, hypothetically, Team A at +150 and Team B at -150. These are illustration prices, not a real market. The table below restates several prices using the formulas above, all on a $100 reference stake, so you can see how differently the two signs behave.

Reading the +150 and -150 rows together, the same $100 stake wins $150 or $66.67, a difference of $83.33 in profit. The favorite compensates with a higher break-even rate of 60% against 40%. If both prices were accurate, the expected value of each bet would be zero: 0.40 times $150 minus 0.60 times $100 is $0 for the underdog, and 0.60 times $66.67 minus 0.40 times $100 is also $0 for the favorite.

Now consider betting $100 on each side of the pair. If Team A wins, the +150 bet profits $150 and the -150 bet loses $100, for a net of +$50. If Team B wins, the -150 bet profits $66.67 and the +150 bet loses $100, for a net of -$33.33. Equal stakes on both sides do not cancel, because the two prices are not symmetric. Offsetting the risk would take unequal stakes, and real sportsbooks never list this exact pair anyway, since their margin changes the numbers on one or both sides.

How to Compare Prices at Equal Risk

When two prices carry different signs, comparing the raw numbers is misleading. The reliable method is to restate both prices on a common basis. One option is equal risk: how much profit does each price earn per $100 risked? At +150 the answer is $150, and at -150 it is $66.67. The other option is equal profit: how much must you risk to earn $100? At +150 that is $66.67, and at -150 it is $150.

Probability is the third common basis. Converting both prices to implied probability puts every bet on one scale from 0% to 100%, which sidesteps the sign problem entirely. Compare the implied probability with your own estimate of the true chance. If you believe an outcome wins 45% of the time and the price implies 40%, the price is worth considering. If the price implies 50%, it is not, even though the payout looks larger. For the reverse conversion, see how to convert probability to betting odds.

Prices also look different in decimal form, where +150 becomes 2.50 and -150 becomes 1.67. The decimal format avoids the sign problem altogether, a trade-off covered in American versus decimal odds. Whichever format you use, remember that an estimate of probability is uncertain. A 45% estimate can easily be 40% or 50% in reality, so a small gap is not proof of value.

Common Misconceptions About Plus and Minus Odds

The first mistake is assuming that +150 is simply the opposite of -150 in payout. It is the opposite only in probability. A bettor who sees -150 and +150 as equal and opposite will overestimate how much a favorite pays or underestimate how often an underdog must win.

The second mistake is reading -150 as three times as likely as +150. In fact 60% is only 1.5 times 40%, so the favorite is a moderate favorite, not a near certainty. A third mistake is believing +100 and -100 are different prices. They are the same price, and a sportsbook may display either one. A fourth is assuming that a favorite is a safer bet in a financial sense. A 60% chance still loses 40% of the time, and the bettor who stakes $150 to win $100 loses more per miss than they gain per win.

Finally, many bettors assume a bigger plus number is automatically better value. A high plus price simply means a lower implied probability. Value depends on the true chance, which neither the sign nor the size of the number reveals. No price removes variance, and none turns betting into dependable income.

Where the Asymmetry Shows Up at the Sportsbook

On a real odds board, the two sides of a market almost never add to 100%. A hypothetical market of +140 on one side and -160 on the other implies 41.67% plus 61.54%, a total of 103.21%. The extra 3.21 points are the margin, which is explained in the article on vig. The asymmetry matters here because a margin applied to the favorite side and the underdog side shows up as different-looking numbers, which makes the cost harder to see.

The asymmetry also shapes how people read line movement. A price move near even money is larger in probability terms than the same move on a long shot, which is why a shift from -110 to -120 is more meaningful than one from +500 to +510. When a price crosses between the two signs, from -105 to +100 for example, the move can look dramatic on the screen while the underlying probability barely changes. Reading prices as probabilities first avoids that trap, and it is also a useful discipline for staking within a budget you can afford to lose.

What to Learn Next

If the +150 and -150 example raised the question of how a sportsbook builds in its margin, the natural next step is the no-vig odds procedure, which strips the margin from a two-sided market. For a market with more than two outcomes, overround across every outcome shows how the same idea scales up. And to see how the break-even idea plays out over a run of bets, read about the break-even win rate. Learning to move between price, probability and payout is the core skill behind every one of these concepts.