How Betting Odds Work

American odds: what the plus and minus mean

US sportsbooks quote American (moneyline) odds. Every price is either a positive or negative number relative to a $100 baseline.

• Negative odds (e.g. -150) show how much you must stake to win $100. At -150 you risk $150 to win $100.
• Positive odds (e.g. +130) show how much you win on a $100 stake. At +130 a $100 bet returns $130 profit.

The favorite carries the minus sign, the underdog the plus. The number's distance from 100 tells you how lopsided the matchup is priced. -110 is close to even; -450 is a heavy favorite; +600 is a long shot.

Your total return is stake plus profit. A winning $50 bet at +200 returns $150 ($50 back plus $100 profit). A winning $50 bet at -200 returns $75 ($50 back plus $25 profit).

Decimal and fractional formats

The same price can be written three ways. Most US apps let you toggle formats, and international soccer markets (Champions League, Serie A, Ligue 1) often default to decimal.

• Decimal: total return per $1 staked, including your stake. +130 = 2.30, -150 = 1.667. Multiply stake by the decimal to get total payout.
• Fractional: profit relative to stake, common in horse racing and UK books. +130 = 13/5, -150 = 2/3.
• American: the +/- format above.

Conversion is mechanical. For positive American odds: decimal = (odds / 100) + 1. For negative: decimal = (100 / |odds|) + 1. So +130 → 1.30 + 1 = 2.30, and -150 → 0.667 + 1 = 1.667. Decimal is the cleanest format for comparing prices across books because you can line up two numbers directly.

Turning odds into implied probability

Every price is a probability in disguise. Implied probability tells you the break-even win rate a bet needs to be profitable.

For negative American odds: probability = |odds| / (|odds| + 100). At -150 that is 150 / 250 = 60.0%.

For positive American odds: probability = 100 / (odds + 100). At +130 that is 100 / 230 = 43.5%.

For decimal: probability = 1 / decimal. A 2.30 price = 1 / 2.30 = 43.5%.

The rule for finding value: if you believe a team wins more often than the implied probability, the price is in your favor. A team you rate at 50% priced at +130 (43.5% implied) is a value bet. A team you rate at 50% priced at -150 (60% implied) is not.

The vig: why the two sides add up to more than 100%

In a fair 50/50 market both sides would sit at +100 (2.00 decimal, 50% each), summing to 100%. Real markets never do. The overround — the amount above 100% — is the sportsbook's margin, also called the vig or juice.

Worked example. A typical two-way NFL total is posted -110 / -110.

• -110 implied probability = 110 / 210 = 52.38%.
• Both sides: 52.38% + 52.38% = 104.76%.
• The overround is 4.76%. That is the gross margin baked into the line.

To recover the true (no-vig) probability, divide each side by the total. 52.38% / 104.76% = 50.0% per side — the fair coin flip you'd expect. The book's 4.76% is what you pay for access, and it compounds on every bet you place.

The same math scales. A three-way soccer market (home / draw / away) might imply 40% + 28% + 37% = 105%, a 5% overround. Lower overround means a fairer price and more of your expected value stays with you.

How margin decides which sportsbook to use

Two books can offer the exact same bet at different implied probabilities. The one with the lower margin pays you more when you win. Over hundreds of bets, a one- or two-point margin difference is the gap between a small edge and a slow bleed.

BETAXIO tracks two figures per book across sampled markets:

• Best-price share — how often that book posts the top price in a market versus its competitors.
• Average margin — the mean overround across sampled markets. Lower is better for you.

Across our sampled US markets, DraftKings led on both metrics: a best-price share of 54.0% over 1,068 sampled markets at an average margin of 4.25%. Fanatics Sportsbook followed with a 41.8% best-price share (466 markets) and the lowest sampled margin at 4.25%. FanDuel posted the top price 36.1% of the time over 596 markets at a 4.46% margin, and Caesars Sportsbook 36.2% over 906 markets but at a higher 5.27% margin.

At the bottom of the sampled group: BetMGM held the top price only 19.9% of the time (438 markets) at a 5.21% margin, and BetRivers sat at 28.3% best-price share (480 markets) with the widest sampled margin at 6.35%. On a -110 bet, the difference between a 4.25% and a 6.35% margin is real money surrendered on every wager. Compare live prices on our betting odds page before you lock in a line.

Reading a worked bet from odds to payout

Put the whole chain together with one bet.

You want to back an NBA underdog at +145.

• Implied probability: 100 / (145 + 100) = 40.8%. The market says this team wins about 4 times in 10.
• Your model rates the team at 46%. Because 46% > 40.8%, the price carries positive expected value.
• Decimal: (145 / 100) + 1 = 2.45.
• Stake $60. Total return if it wins = 60 × 2.45 = $147, i.e. $60 back plus $87 profit.

Now the value calculation. Expected value = (win probability × profit) − (loss probability × stake) = (0.46 × 87) − (0.54 × 60) = 40.02 − 32.40 = +$7.62 per $60 bet. Positive EV means the bet is worth making at that price. Shop the same +145 across books — if one has it at +150, your EV rises further at zero extra risk. That is the entire reason line shopping works.

How odds move: opening line vs current price

Odds are not fixed. A book opens a market at an estimated price, then adjusts as money arrives and information changes — injuries, weather, lineup news, or sharp bets on one side. When a line moves from -110 to -130, the implied probability climbed from 52.4% to 56.5%, and the price got worse for that side.

Tracking opening versus current lines tells you where the market is heading. A steadily shortening favorite signals confidence flowing to that side; a drifting underdog is getting cheaper. Our market movers feed follows these shifts. If you catch a value price before the market corrects, you lock in the better implied probability — the number moving after you bet does not change your ticket.