What does decimal odds 2.50 mean?

Decimal odds show the total amount returned per 1 unit staked, including your stake back. At 2.50 a winning 10 stake returns 25 in total, which is 15 profit plus your 10 back. To get the profit only, subtract 1: 2.50 means 1.50 profit per 1 staked. Decimal is the default across Europe and on most betting exchanges because the maths is the simplest of the three formats.

How do American odds +150 and -200 work?

American (moneyline) odds are quoted around a 100 unit base. A positive number like +150 is the profit on a 100 stake, so +150 returns 150 profit plus your 100 back, equal to decimal 2.50. A negative number like -200 is the stake needed to win 100, so you risk 200 to win 100, equal to decimal 1.50. Positive numbers mark underdogs, negative numbers mark favourites, and -110 is the typical price on a near coin-flip after the vig.

What does fractional odds 3/2 mean?

Fractional odds, common in the UK and in horse racing, show profit over stake as a reduced fraction. 3/2 (said 'three to two') means you win 3 for every 2 staked, so a 2 stake returns 5 in total. To convert to decimal, divide and add 1: 3 / 2 + 1 = 2.50. Even money is written 1/1 and equals decimal 2.00. Odds-on prices where the favourite pays less than even, like 1/2, mean you win 1 for every 2 staked.

How is implied probability calculated from odds?

Implied probability is simply 1 divided by the decimal odds, written as a percent. Decimal 2.00 gives 1 / 2.00 = 50%, decimal 2.50 gives 40%, and decimal 1.50 gives about 66.7%. It is the chance the price is pricing in. Shorter odds mean a higher implied probability. To go the other way, fair decimal odds equal 100 divided by your probability percent, so a 25% chance is fair at decimal 4.00.

What is the vig and why do probabilities add up to over 100%?

If you total the implied probabilities of every outcome in a market, the sum is more than 100%. That extra slice is the overround, or vig, the bookmaker's built-in margin. A fair coin should pay 2.00 on each side (50% + 50% = 100%), but a book offering 1.90 on each side implies 52.6% + 52.6% = 105.3%, so the vig is about 5.3%. The vig is why the displayed implied probability is always a little higher than the true fair chance.

Compare a price across a UK and a US sportsbook

One book quotes 3/2, another quotes +150, and a third lists 2.50. Without a converter they look like three different things. Drop any one into the tool and the other two appear, all showing the same 40% implied probability, so you can see at a glance which book is offering the better number and which is just dressing up the identical price in a different format.

Sanity-check your own model against the market

You ran the numbers and think a team has a 55% chance to win. Enter 55 in the probability field and the tool returns the fair decimal odds of about 1.82. If the market is offering 2.10, the price is longer than your model says it should be, which is exactly the gap a probability person looks for before deciding anything.

Learn how the three odds formats relate

Switching countries or sites and seeing odds written a new way is confusing the first few times. Type a price you already understand, watch how it maps to the format you do not, and the relationship clicks: even money is 2.00, is 1/1, is +100, is 50%. A few minutes here saves a lot of squinting at unfamiliar boards later.

Estimate the bookmaker margin on a market

Convert each side of a two-way market to its implied probability and add them up. If the total comes to 105% instead of 100%, that 5% is the vig. Doing this across a few books tells you which one prices the tightest margin, which over many bets is the single thing that matters most for anyone tracking value rather than chasing a tip.

Odds Converter with Implied Probability

Decimal, fractional and American odds with implied probability, all four update live as you type

Runs locally
Category Calculator
Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Enter odds as

Decimal

Equivalent odds

Decimal: 2.5
Fractional: 3/2
American: +150
Implied probability: 40%

About implied probability and the vig

Implied probability is 1 / decimal odds. Add up the implied probabilities on every outcome of a market and the total comes to more than 100%. That overround is the bookmaker margin, the vig. On a fair coin both sides should pay 2.00 (50% each); a book that offers 1.90 each is pricing in about 5.3% of vig.

For information only. Odds describe price, not a tip. Bet within your means and only if it is legal where you are.

What this tool does

A free odds converter that turns any betting price into all the others: decimal (European, like 2.50), fractional (UK, like 3/2), American (moneyline, like +150 or -200) and the implied probability the price encodes. Type a value in one format and the other three appear instantly, so you can compare a UK book quoting 3/2 against a US book quoting +150 and see they are the same 40% chance. It works the other way too: enter a probability and read back the fair decimal odds, which is handy for sanity-checking your own model against the market. The tool explains what each format means, shows how implied probability is calculated, and describes the bookmaker margin (the vig) that makes a market's probabilities add up to more than 100%. One click copies all four formats. Everything runs in your browser; this is an information and education tool, it does not place bets, suggest stakes, or link to any sportsbook.

Tool details

Input: Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 9 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Finance; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How Odds Converter fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Compare a price across a UK and a US sportsbook
One book quotes 3/2, another quotes +150, and a third lists 2.50. Without a converter they look like three different things. Drop any one into the tool and the other two appear, all showing the same 40% implied probability, so you can see at a glance which book is offering the better number and which is just dressing up the identical price in a different format.
Sanity-check your own model against the market
You ran the numbers and think a team has a 55% chance to win. Enter 55 in the probability field and the tool returns the fair decimal odds of about 1.82. If the market is offering 2.10, the price is longer than your model says it should be, which is exactly the gap a probability person looks for before deciding anything.
Learn how the three odds formats relate
Switching countries or sites and seeing odds written a new way is confusing the first few times. Type a price you already understand, watch how it maps to the format you do not, and the relationship clicks: even money is 2.00, is 1/1, is +100, is 50%. A few minutes here saves a lot of squinting at unfamiliar boards later.
Estimate the bookmaker margin on a market
Convert each side of a two-way market to its implied probability and add them up. If the total comes to 105% instead of 100%, that 5% is the vig. Doing this across a few books tells you which one prices the tightest margin, which over many bets is the single thing that matters most for anyone tracking value rather than chasing a tip.

Common pitfalls

Reading implied probability as a true probability. The 40% shown for decimal 2.50 already includes the bookmaker margin, so the real fair chance is a little lower. Compare implied probabilities across books to gauge the vig before treating any single number as the actual odds of the event.
Mixing up American favourites and underdogs. A plus sign like +150 is the underdog (profit on a 100 stake), a minus sign like -200 is the favourite (stake to win 100). Flipping the sign in your head turns a 40% price into a 67% one, which is a big mistake when comparing books.
Forgetting that fractional odds show profit, not total return. 3/2 means win 3 on a 2 stake, so the total back is 5, not 3. Adding the stake is what turns 3/2 into decimal 2.50; treating the fraction itself as the multiplier undercounts every payout.

Privacy

Every conversion runs as plain JavaScript inside your browser tab. The odds you type, the formats you switch between and the implied probabilities are all computed locally and never sent anywhere; there is no logging of what you entered. The one thing to know: the shareable URL encodes your input value and chosen format in the query string, so a link you paste into chat will record that price in the recipient server's access log. That is harmless for a public price, but if you would rather not, use the copy button and paste the text instead of sharing the URL.

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Odds Converter with Implied Probability

About implied probability and the vig

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Odds Converter fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Compare a price across a UK and a US sportsbook

Sanity-check your own model against the market

Learn how the three odds formats relate

Estimate the bookmaker margin on a market

Common pitfalls

Privacy

FAQ

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