Plus Minus Odds to Probability: Convert American Odds to Win Chance (Calculator Guide)

How-To · Updated 23 Oct 2026 · By the BetGabay Editorial Team

Every odds number hides a percentage. -150 is really saying "about 60%." +300 is saying "about 25%." Once you can see those percentages, you stop asking "who will win?" and start asking the question that actually matters in betting: is this price fair?

This guide shows you how to convert plus/minus odds into probability, strip out the bookmaker's margin, and use the result to judge value. If you're new to American odds, read plus minus odds explained first, and for an overview of all formats, see betting odds explained.

Kaugnay na gabay: Betting Odds Explained: A Clear Guide for Filipinos

The two formulas you need

Every American odds number converts to an implied probability with one of two simple formulas:

• Minus odds (favourites): implied probability = odds ÷ (odds + 100), ignoring the minus sign.
• Plus odds (underdogs): implied probability = 100 ÷ (odds + 100).

Multiply by 100 to get a percentage. That's it. Everything else on this page builds on these two lines.

Step by step: minus odds

Take -150.

1. Drop the minus sign: 150.
2. Add 100: 150 + 100 = 250.
3. Divide: 150 ÷ 250 = 0.60.
4. Convert to a percentage: 60%.

So -150 says the bookmaker prices that outcome at about a 60% chance. Another example: -250 → 250 ÷ 350 = 71.4%. And -110 → 110 ÷ 210 = 52.4%, which is why 52.4% is the famous break-even rate for standard spread bets.

Step by step: plus odds

Take +200.

1. Add 100 to the odds: 200 + 100 = 300.
2. Divide 100 by that: 100 ÷ 300 = 0.333.
3. Convert: 33.3%.

More examples: +150 → 100 ÷ 250 = 40%. +400 → 100 ÷ 500 = 20%. +1000 → 100 ÷ 1100 = 9.1%.

Shortcut through decimal odds

If your sportsbook shows decimal odds, the formula is even simpler: implied probability = 1 ÷ decimal odds. So 1.67 → 59.9%, 2.50 → 40%, 4.00 → 25%. You can also convert American to decimal first (see our plus minus odds explained guide) and then divide 1 by the result. Both routes give the same answer, allowing for rounding.

Full conversion table

Use this as a quick reference. The last column shows the odds expressed as "x to 1 against," another way of describing the same chance.

Why both sides add up to more than 100%

Look at a typical NBA moneyline: Team A -180, Team B +155.

• Team A: 180 ÷ 280 = 64.3%
• Team B: 100 ÷ 255 = 39.2%
• Total: 103.5%

In a fair world, the chances of all outcomes add up to exactly 100%. The extra 3.5% is the bookmaker's margin, also called the overround, vig or juice. It's how the book makes money regardless of who wins: it pays out slightly less than fair odds on every side.

On a spread with -110 on both sides, each side implies 52.4%, for a total of 104.8%. The margin is about 4.5% of turnover. On player props and futures, margins are often larger.

Removing the vig: finding the "fair" probability

Because implied probabilities include margin, they slightly overstate every outcome's chance. To estimate the market's true view, you can strip out the margin. The simplest method is proportional normalisation: divide each implied probability by the total.

Using Team A 64.3% and Team B 39.2% (total 103.5%):

• Team A fair probability: 64.3 ÷ 103.5 = 62.1%
• Team B fair probability: 39.2 ÷ 103.5 = 37.9%

Now they add up to 100%. The corresponding fair odds would be about -164 for Team A and +164 for Team B. Comparing the posted odds to these fair odds shows exactly how much margin you're paying on each side.

There are more advanced methods, such as allocating more margin to long shots (because books often shade them more), but proportional normalisation is a good, easy starting point for two-way markets.

Three-way markets: football 1X2

In football, the match result market has three outcomes: home win, draw, away win. Same method, just three numbers. Suppose odds are Home +140, Draw +230, Away +200.

• Home: 100 ÷ 240 = 41.7%
• Draw: 100 ÷ 330 = 30.3%
• Away: 100 ÷ 300 = 33.3%
• Total: 105.3%

Normalising gives Home 39.6%, Draw 28.8%, Away 31.6%. Three-way markets tend to carry more margin than two-way ones, so it's worth checking before you bet. For the decimal version of these calculations, see decimal odds explained.

Futures and many-outcome markets

Championship futures may list 10, 20 or 30 teams. Convert every price and add them up, and you'll often see totals of 120% to 150% or even more. That means the average bet carries a large margin. A team at +800 implies 11.1%, but after removing a 30% overround, the market's fair view might be closer to 8.5%. Futures can be fun, but this is why many careful bettors keep futures stakes small and focus on single games where margins are tighter.

From probability back to odds

Sometimes you start with your own estimate and want to know what odds would be fair. The reverse formulas:

• If probability is above 50%: American odds = -(p ÷ (1 - p)) × 100. For 70%: -(0.70 ÷ 0.30) × 100 = -233.
• If probability is below 50%: American odds = ((1 - p) ÷ p) × 100, shown with a plus. For 25%: (0.75 ÷ 0.25) × 100 = +300.
• Exactly 50%: +100.
• Decimal: 1 ÷ p. For 40%: 2.50.

Knowing your fair odds lets you decide quickly whether a posted price is worth taking. If you think a team wins 45% of the time, fair odds are about +122. If the book offers +140, that's better than fair. If it offers +105, it's worse.

Expected value: putting probability to work

Implied probability becomes truly useful when you compare it with your own estimate. That comparison gives you expected value (EV), the average result of a bet if you could repeat it many times.

The formula with decimal odds: EV = (your probability × (decimal odds - 1)) - (1 - your probability), per unit staked.

Example 1: Positive EV

Odds +150 (2.50). Implied 40%. You estimate 45%.

EV = 0.45 × 1.50 - 0.55 = 0.675 - 0.55 = +0.125. That's +12.5% per unit. On ₱1,000 stakes, you'd expect to gain about ₱125 per bet on average, if your estimate is right.

Example 2: Negative EV

Odds -200 (1.50). Implied 66.7%. You estimate 62%.

EV = 0.62 × 0.50 - 0.38 = 0.31 - 0.38 = -0.07. That's -7% per unit. Even though the team is likely to win, the price is too short.

This is the key lesson: a likely winner can be a bad bet, and an unlikely winner can be a good one. It all depends on the price relative to the real chance.

Break-even win rates for common prices

The break-even rate is just the implied probability. If you can't realistically win at that rate on a given type of bet, the price isn't for you.

Parlay probability

To find the implied probability of a parlay, multiply the probabilities of each leg (assuming they're independent). Three legs at -110 each: 0.524 × 0.524 × 0.524 = 14.4%. The parlay pays about +596, which implies 14.4%, but the fair probability after removing each leg's margin is 0.5 × 0.5 × 0.5 = 12.5%. In other words, parlays compound the bookmaker's margin. A five-leg parlay at -110 per leg implies 3.9% but has a fair chance of only 3.1%. Our ano ang parlay guide explains this in Taglish.

How to estimate your own probability

Implied probability is the market's view. To find value, you need your own view, and that's the hard part. A few practical approaches:

• Start from the market. Use the no-vig probability as a baseline, then adjust for information you believe the market hasn't fully priced, such as a late injury or a scheduling disadvantage.
• Use simple ratings. Track point differential or efficiency for teams over recent games, adjust for home court, and convert expected margins into win chances.
• Be specific. Write your estimate down as a number before you look at odds, to avoid anchoring on the bookmaker's price.
• Stay humble. Markets for popular games like the NBA are efficient. Edges are usually small, and a 2 to 3 percentage point edge is already meaningful.

Checking whether you're well calibrated

Calibration means that when you say 60%, things happen about 60% of the time. To test it, record your estimates for many bets, then group them: all your 55–60% picks, all your 60–65% picks, and so on. Compare your estimated rates with what actually happened. If your "60% picks" only win 52% of the time, you're overconfident and should shade your estimates toward the market. This simple exercise does more for long-term results than any tipster subscription.

Closing line value

Another way to measure skill is to compare the odds you took with the odds right before the game, the closing line. If you regularly get better prices than the close (for example, you bet +150 and it closes at +130), your bets were priced better than the market's final, most informed view. Over time, beating the closing line is strongly linked with profit, even if short-term results are noisy.

Bankroll sizing using probability

Once you have an edge estimate, the next question is how much to bet. One well-known approach is the Kelly criterion, which sets stake size based on edge and odds: stake fraction = (b × p - q) ÷ b, where b is decimal odds minus 1, p is your win probability and q is 1 - p.

Example: +150 (b = 1.5), your p = 0.45, q = 0.55. Kelly = (1.5 × 0.45 - 0.55) ÷ 1.5 = 0.125 ÷ 1.5 = 8.3% of bankroll.

Full Kelly is aggressive and assumes your estimates are accurate, which they rarely are. Many bettors use a quarter or half Kelly, or simply a flat 1 to 2 percent per bet. If you're unsure, flat staking is the safer choice.

Doing it in a spreadsheet

If you track bets in Google Sheets or Excel, these formulas save time. With American odds in cell A2:

• Implied probability: =IF(A2<0, -A2/(-A2+100), 100/(A2+100))
• Decimal odds: =IF(A2<0, 1+100/-A2, 1+A2/100)

With your own probability in B2 and decimal odds in C2, EV per unit: =B2*(C2-1)-(1-B2). Add a column for the closing odds and you have a basic but powerful betting log.

Worked examples from Filipino favourite sports

PBA moneyline

Team A -170, Team B +145. Implied: 63.0% and 40.8% (total 103.8%). No-vig: 60.7% and 39.3%. If you believe Team B's import gives them a 45% chance, +145 offers value: EV = 0.45 × 1.45 - 0.55 = +0.10.

NBA spread

Both sides -110. Implied 52.4% each. If you think the favourite covers 55% of the time, EV = 0.55 × 0.909 - 0.45 = +0.05. Small, but positive.

Boxing

Fighter X -400, Fighter Y +300, Draw +2000. Implied: 80.0%, 25.0%, 4.8% (total 109.8%). The large overround is typical for fights with a draw option. No-vig: 72.9%, 22.8%, 4.3%. For real-world fight pricing, see Manny Pacquiao betting odds history.

MLBB match winner

Team Blue -250, Team Red +190. Implied: 71.4% and 34.5% (total 105.9%). No-vig: 67.4% and 32.6%. In best-of-three formats, underdogs win single maps fairly often, so these markets sometimes leave room for disciplined underdog bets. See MLBB odds explained.

Asian odds formats and probability

Some Asian sportsbooks show odds in Hong Kong, Malay or Indonesian formats, which Filipino bettors may run into on regional sites. All of them convert to probability once you turn them into decimal.

• Hong Kong odds show profit per unit staked. HK 0.80 equals decimal 1.80, so implied probability is 1 ÷ 1.80 = 55.6%.
• Malay odds range from -1 to +1. A positive Malay number works like HK odds: +0.80 equals decimal 1.80. A negative Malay number shows how much you risk to win one unit: -0.80 means risk 0.80 to win 1, equal to decimal 2.25 and an implied 44.4%.
• Indonesian odds mirror American odds divided by 100. Indo -1.50 equals American -150 (60%), and Indo +2.00 equals American +200 (33.3%).

The method never changes: get to decimal, then divide 1 by it. Once you can do that, no odds format can confuse you.

Probability for spreads and totals

Spreads and totals usually sit near -110 on both sides, which implies roughly 50/50 after removing margin. That's by design: the line itself does the balancing. When a book moves a spread side to -125 and the other to +105, it's telling you the market now leans to one side slightly. Convert both: -125 is 55.6% and +105 is 48.8%. Total 104.4%. No-vig: 53.3% and 46.7%. That small shift can be enough to decide whether a bet still offers value at the posted line or whether you'd rather wait for a better number.

You can also think about the probability of different margins. In basketball, each point of spread near the middle of the distribution is worth roughly 3 percentage points of cover probability. So if you believe the fair spread is -4 and the book offers -2.5, you may have a cover probability several points above 50%. This is approximate, but it's a useful mental model for judging how much a half point or full point matters.

The favourite–long shot bias

Research across many betting markets has found a tendency for long shots to be overpriced relative to their true chances, while heavy favourites are often priced closer to fair. People enjoy the thrill of a big payout and overbet unlikely outcomes; books respond by shading those prices further. In practice, this means a +2000 outcome may have a true chance well below its implied 4.8%. It doesn't mean favourites are always good bets, only that long shots tend to carry hidden extra margin. Keep that in mind when a big plus number looks tempting.

Variance: what probability means for losing streaks

Understanding probability also means understanding streaks. If you win 55% of your bets, the chance of losing five in a row on any given run of five bets is 0.45 to the fifth power, about 1.8%. That sounds rare, but over a season of several hundred bets, you're almost certain to hit a five-game losing streak at some point, and quite likely a seven- or eight-game one too. Many bettors give up on a sound approach during a normal losing streak, or double their stakes to "get it back." Knowing the maths helps you stay calm and stick to your staking plan.

A useful exercise: calculate the probability of different streak lengths for your typical win rate and number of bets. You'll find long streaks are far more common than intuition suggests. That's not bad luck; it's simply how probability works.

Probability in live betting

Live odds update with every event in a game, and the implied probability moves with them. If a favourite at -200 (66.7%) falls behind by ten points early, its live odds might drift to +120 (45.5%). Whether that's value depends on how much the early deficit truly changes the chances. In basketball, an early ten-point lead is less decisive than many fans think, because there are so many possessions left. In football, a single goal changes probabilities a lot more because scoring is rare. Thinking in probabilities helps you judge whether the market has overreacted or underreacted, but remember that live margins are often wider and streams can lag behind the real action. See our live betting tips for practical guidance.

Correlated outcomes and same-game parlays

The parlay maths above assumes legs are independent. In a same-game parlay, they often aren't. If a team wins by a lot, the game total may also be more likely to go over, and a star player may be more likely to hit his points prop. Books know this and adjust same-game parlay prices, usually with extra margin. Multiplying the individual implied probabilities will overstate the true chance of related outcomes happening together, or understate it, depending on the correlation. Treat same-game parlays as entertainment rather than a place to hunt for value unless you've studied correlations carefully.

Probability vs house edge in casino games

Casino games make probability concrete because the rules fix it. In European roulette, a single-number bet has a 1 in 37 chance (2.7%) but pays 35 to 1, which would require a 2.8% chance to break even. The gap is the house edge of about 2.7%. In baccarat, the Banker bet wins slightly more often than Player, which is why a commission is charged on Banker wins. Sports betting differs in one key way: the true probabilities aren't fixed or published, so skilled bettors can sometimes find prices that are better than fair. In a casino, the edge always favours the house.

Glossary

• Implied probability: the chance suggested by the odds, including margin.
• No-vig (fair) probability: implied probability after removing the margin.
• Overround: the total of all implied probabilities above 100%.
• Vig / juice: the bookmaker's cut.
• Expected value (EV): average profit or loss per unit over many repetitions.
• Break-even rate: win rate needed to neither profit nor lose at a given price.
• Closing line value (CLV): getting better odds than the final pre-game price.
• Calibration: how closely your estimated probabilities match actual results.
• Kelly criterion: staking formula based on edge and odds.

Comparing prices across sportsbooks with probability

Probability gives you a clean way to compare offers. Suppose three books price the same NBA underdog at +140, +150 and +135. Converted, those are 41.7%, 40.0% and 42.6%. The lowest implied probability, +150, is the best price for you as the bettor, because you're paying for a smaller chance. Over a season, consistently taking the best available number can be worth several percentage points of return, which is often the difference between a small profit and a small loss. Even if you only have accounts at two legitimate books, checking both before each bet is one of the simplest improvements you can make.

How bookmakers use probability

Bookmakers start with their own estimate of the true probabilities, often built from models, data feeds and expert traders. They convert those to fair odds and then apply a margin. As bets arrive, they adjust prices to manage risk and to reflect information from respected bettors. A book that takes heavy action from sharp customers on one side will move that price quickly. That's why the closing line tends to be a good estimate of the true probability for popular events: it reflects all the information and money that came in before the start.

Practice problems

1. Convert -175 to probability. 175 ÷ 275 = 63.6%.
2. Convert +325 to probability. 100 ÷ 425 = 23.5%.
3. Team A -130, Team B +110. What's the overround? 56.5% + 47.6% = 104.1%, so 4.1%.
4. No-vig probability for Team B in question 3? 47.6 ÷ 104.1 = 45.7%.
5. You estimate 30% for an outcome priced at +275. Is it value? Implied is 26.7%, so yes: EV = 0.30 × 2.75 - 0.70 = +0.125.
6. What are fair odds for a 65% chance? -(0.65 ÷ 0.35) × 100 = -186.

Work through these a few times and the conversions will become automatic.

Probability and the PBA or UAAP calendar

Local leagues bring their own patterns that affect true probabilities. In the PBA, import changes in reinforced conferences can swing a team's chances overnight, and markets sometimes take a game or two to adjust fully. Elimination-round games late in a conference may involve teams that have already secured or lost a playoff spot, changing motivation. In the UAAP and NCAA, young rosters produce more variance from game to game, so implied probabilities of heavy favourites may overstate their true reliability. None of these factors guarantee value, but they're exactly the kind of context where a careful bettor's estimate can differ from the market's. Write down your reasoning along with your probability, so you can check later whether the factor really mattered.

A simple routine to use before every bet

1. Write your own probability estimate before looking at prices.
2. Check the odds at every book you use and note the best price.
3. Convert to implied probability and remove the vig.
4. Compare with your estimate and calculate EV.
5. Bet only when EV is clearly positive, using a fixed, modest stake.
6. Record the price you took and the closing price.

It takes a minute per bet, and it turns betting from guesswork into a repeatable process.

Common mistakes

1. Treating implied probability as truth. It's the book's price, margin included.
2. Forgetting to remove the vig before comparing with your estimate.
3. Confusing "likely" with "good value." A 75% favourite at -400 is a bad bet if it's really 75%.
4. Overestimating your edge. Small samples mislead; calibrate over hundreds of bets.
5. Ignoring compounding margin in parlays.
6. Using full Kelly with shaky estimates.

Taglish recap

Para gawing tsansa ang minus odds: hatiin ang odds (walang minus) sa odds plus 100. Ang -150 ay 150 ÷ 250 = 60%. Para sa plus odds: hatiin ang 100 sa odds plus 100. Ang +200 ay 100 ÷ 300 = 33.3%. Kapag pinagsama mo ang tsansa ng dalawang panig, lalampas sa 100%; iyon ang tubo ng bookie. Para malaman kung may value ang taya, ikumpara ang sarili mong tantya sa tsansang galing sa odds. Kung mas mataas ang tantya mo, positibo ang expected value. Pero mag-ingat: madalas sobrang kumpiyansa ang mga bettor sa sarili nilang tantya.

Responsible betting

Probability maths helps you avoid bad prices, but even positive-EV bettors face long losing streaks. Never bet money you need for bills, set deposit limits, and take breaks. If betting stops being fun, our responsible gambling page lists free, confidential help.