Odds express both a payout and a market-implied chance. This guide shows how to convert FanDuel-style American and decimal odds into implied probability, check results, and normalize for the bookmaker margin. You will find the exact formulas, replicated worked examples, and a short checklist to build or test a simple fanduel odds calculator in a spreadsheet or small tool.

American, decimal, and implied probability are different views of the same market price.

Use p = 100/(odds+100) for positive American lines and p = |odds|/(|odds|+100) for negative lines.

Normalize implied probabilities to remove the bookmaker margin when you need fair comparisons.

What 'odds' mean and the common formats you will see

Odds are two things at once: a price you can take or offer, and a way to express an implied probability. A posted line tells you how much a winning stake will return and, when converted, what the bookmaker is implying about the chance of that outcome. Use a fanduel odds calculator to see both views: the payout side and the implied-probability side in one glance.

Bookmakers present odds in different formats so customers in different regions can read them easily. The three formats you will commonly see are American (moneyline), decimal, and the implied probability expressed as a percentage. Each format shows the same underlying information, but the numbers look different and require simple conversions to move between them.

American, or moneyline, odds use a plus sign for underdogs and a minus sign for favorites; decimal odds show total return per unit stake; implied probability expresses the market price as a percent chance. For readers in the United States, FanDuel and many major sites default to American odds but allow the display to switch to decimal; changing the display does not change the math behind the numbers, only how they appear, so conversions remain consistent regardless of what you see on screen FanDuel help center.

Odds serve three practical purposes. First, they tell you how much you would receive if your selection wins. Second, they express a market view that can be converted into implied probability for model inputs or comparisons. Third, they embed the bookmaker margin, which affects how you compare prices across sites. Understanding these roles makes it easier to use an odds calculator correctly.

Common-format examples help anchor the idea: American +150 means an underdog price you would win 150 for a 100 stake; decimal 2.50 means a 1-to-2.5 total return including stake; an implied probability of 40.0% would represent the same market view. Those numerical links between formats are fixed and reversible with simple formulas.

How do I calculate the odds?

Convert moneyline to decimal, then compute implied probability as 1/decimal; for American moneyline use the formulas for positive and negative lines, and normalize for vig when needed.

Core formulas: how to convert American and decimal odds to implied probability

For positive American odds (plus numbers), the implied probability formula is p = 100 / (odds + 100). A copy-paste version is easier to use in a calculator: p = 100/(+odds+100). That formula and explanation follow the standard industry approach to implied probability conversion Investopedia implied probability guide. You can also check other implied-probability calculators such as GamingToday.

For negative American odds (minus numbers), use the absolute value in the formula: p = |odds| / (|odds| + 100). In practice you remove the minus sign and apply the same structure so the math stays clear and consistent. This negative-line formula is the conventional method used across educational betting resources Pinnacle guide to implied probability.

Decimal odds convert to implied probability with the simple rule p = 1 / decimal. That gives the probability of the outcome implied by the decimal number. To go from moneyline to decimal, use these quick rules: for positive moneyline, decimal = 1 + moneyline/100; for negative moneyline, decimal = 1 + 100/|moneyline|. Those two-step conversions keep your spreadsheet logic straightforward and reversible Odds reference.

Below are two one-line worked instances you can copy into a calculator: a positive example +150 gives p = 100/(150+100) = 0.400 or 40.0%. The same +150 as decimal is 1 + 150/100 = 2.50, and decimal implied probability is 1/2.50 = 0.400. A negative example -200 gives p = 200/(200+100) = 0.667 or 66.7% and decimal 1 + 100/200 = 1.50, which in turn yields 1/1.50 = 0.667. Use a single reference when presenting these formulas so each paragraph stays tightly sourced Pinnacle guide to implied probability.

Step-by-step: using a fanduel odds calculator to check conversions

Screenshot of a small spreadsheet converting +150 and -200 odds into decimal and implied probability using fanduel odds calculator on a dark minimalist Funded Plays style background

Start by deciding which input format you have: American positive, American negative, or decimal. A simple fanduel odds calculator or a free converter such as Covers free odds converter should accept any of the three and return the implied probability plus the decimal equivalent so you can validate both directions. Accept either sign-based moneyline input or a decimal number and let the tool normalize the value.

Checklist of inputs to build or test in a small calculator or spreadsheet: enter the moneyline exactly as displayed (including the plus or minus), or enter the decimal number, and request two outputs: implied probability and the alternate odds format. The calculator should apply the formulas from the previous section to produce results you can cross-check.

Manual validation is straightforward. If you input +150, check that the calculator shows decimal 2.50 and implied probability 40.0% using p = 100/(150+100). If you input -200, confirm decimal 1.50 and implied 66.7% via p = 200/(200+100). A two-way check helps catch format mistakes quickly.

Convert American or decimal odds into implied probability and decimal equivalent

Paste American odds with sign or decimal and compute the implied probability

Set up two spreadsheet cells for the conversion formulas: one cell that normalizes a moneyline into decimal using the moneyline-to-decimal rules, and another that computes implied probability as 1/decimal. That two-cell approach gives you both the decimal number and the percentage, and it is easy to audit with known examples.

Remember that FanDuel offers a display setting toggle between American and decimal formats; the calculator you build should accept either form as input because the underlying math is the same regardless of which display the app shows the user FanDuel help center.

Converting formats in practice and quick reference charts

Fast rule summary you can memorize: for positive moneyline M use decimal = 1 + M/100; for negative moneyline -M use decimal = 1 + 100/M. Then implied probability is p = 1/decimal. Keep these three short lines in your head or in a tiny reference cell in your spreadsheet for quick checks.

Here are immediate conversions you can copy into a cheat sheet: +150 -> decimal 2.50 -> implied 40.0%. -200 -> decimal 1.50 -> implied 66.7%. These two examples are useful test cases to confirm your odds-conversion chart matches the industry formulas Pinnacle guide to implied probability. For a quick online calculation you can also try the OmniCalculator implied probability tool at OmniCalculator.

For a small printable table include common prices such as +110, +150, +200, -110, -150, -200 and their decimal and probability equivalents. Reproducing a three-column chart in a spreadsheet makes spot checks quick and reduces the risk of misreading the sign or doing a double conversion.

When comparing markets, remember that display settings do not alter the underlying math; converting between formats is strictly arithmetic. If you see different-looking numbers across apps, run them through your conversion cell to verify whether the markets actually disagree or simply use a different presentation style Odds reference.

Overround and the bookmaker margin: why implied probabilities exceed 100%

Posted odds include the bookmaker margin, often called the vig or overround, which is why implied probabilities across all mutually exclusive outcomes usually sum to more than 100%. That excess is how the bookmaker builds in a profit margin and why raw implied probabilities are not direct probabilities of real-world events Smarkets overround explanation.

To see the overround in practice, use your calculator on both sides of a two-outcome market and add the implied probabilities. A simple two-outcome test often shows a total above 100%, exposing the built-in market margin. Spotting that excess is the first step to normalizing prices for fairer comparisons.

Test conversions with FundedPlays challenge-style markets

Try a quick conversion in your calculator or spreadsheet now to see the overround on a real market; compare both sides and note how the total exceeds 100 percent, then use normalization if you need cleaner model inputs.

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A basic no-vig adjustment for a two-outcome market normalizes the implied probabilities by dividing each implied probability by the total implied probability sum. For example, if two implied probabilities add to 105%, divide each by 1.05 to rescale them so the normalized probabilities sum to 100%.

Use no-vig normalization when you build models or compare prices across bookmakers; however, remember that removing the vig does not improve the predictive power of the quoted market probabilities, it only rescales them for comparison purposes Pinnacle guide to implied probability.

Common mistakes and troubleshooting when you calculate odds

The most frequent error is misreading negative lines and forgetting to use the absolute value in formulas. Always strip the minus sign and treat the magnitude as the input when applying the negative-line formula; that prevents sign errors and gives consistent implied probabilities Investopedia implied probability guide.

A second common problem is double conversion: converting a decimal to moneyline and back again, or applying the decimal formula twice. To avoid this, pick a canonical internal format in your spreadsheet (decimal is often simplest) and convert inputs into that format before doing probability math.

Rounding can also hide small differences, especially when normalizing for vig. Use a few extra decimal places while you calculate and only round for display. Finally, verify your tool with worked examples such as +150 and -200 to confirm you implemented both positive and negative formulas correctly.

Worked examples: +150, -200 and real-case scenarios

Worked example for +150. Step 1: convert moneyline to decimal: decimal = 1 + 150/100 = 2.50. Step 2: implied probability = 1/2.50 = 0.400 or 40.0%. These steps are direct applications of the positive-moneyline formulas discussed earlier Pinnacle guide to implied probability.

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Worked example for -200. Step 1: remove the minus and convert to decimal: decimal = 1 + 100/200 = 1.50. Step 2: implied probability = 1/1.50 = 0.667 or 66.7%. These calculations mirror the formulas used by educational resources and match common examples used to verify calculators.

For three-way markets, such as soccer match outcomes (home, draw, away), apply the same conversions to each price and then observe the overround when you sum the implied probabilities. The normalization step rescales them to 100% if you need no-vig comparisons for modeling. For how we evaluate markets in practice, see our analysis on how Funded Plays evaluations work.

Putting it together: when to use these conversions and next steps

Practical uses for these conversions include inserting implied probabilities into forecasting models, comparing prices across markets, and identifying potential value where your model's probability differs materially from the normalized market price. Keep conversions reproducible so you can audit your inputs. Learn more at Funded Plays.

Next steps for a reader: build a small spreadsheet that accepts moneyline or decimal input, computes decimal and implied probability outputs, and includes a normalization cell for no-vig adjustments. Validate the sheet with the worked examples in this guide before relying on it for analysis. See more on our blog.

Finally, always treat posted odds as market prices that include margin. Use conversions and normalization to aid comparison and modeling, but do not treat implied probability as a guaranteed forecast of the real-world outcome.

What is implied probability?

Implied probability is the market's converted chance for an outcome derived from posted odds. It converts odds into a percentage that represents how the market prices the outcome.

How do I convert American odds to decimal?

For positive moneyline M use decimal = 1 + M/100. For negative moneyline -M use decimal = 1 + 100/M. Then implied probability is 1/decimal.

What is a no-vig adjustment?

A no-vig adjustment rescales implied probabilities so they sum to 100% by dividing each implied probability by the total implied probability sum, useful for model comparisons.

Use the formulas and checks in this article to validate any odds you see on a betting-display and to produce clean inputs for models. Always remember that posted odds include a margin and are market prices rather than perfect probabilities. If you want a practical place to test prediction skills in a structured format, consider reviewing the challenge options on the FundedPlays Challenges page to understand how skill-based evaluation programs present market-like decision problems.