Understanding Betting Odds Formats: Fractional, Decimal, and American Explained

This guide provides a simple breakdown of betting odds formats. You’ll see how to read them, how they work, and what each format means. We’ll use real numbers and quick examples you can apply across sports — from soccer and tennis to cricket and esports. 

Most sportsbooks, including TonyBet, allow you to switch formats in settings. If you prefer a calculator, keep one handy when you compare prices across books.

Fractional Odds (UK Style): How to Read and Calculate

Fractional odds display potential profit relative to your stake, written as numerator/denominator. The numerator shows profit, while the denominator shows the required stake. For example, odds of 5/1 mean you’ll win five units of profit for every one unit staked and receive your original stake back.

• Payout: Stake × (numerator/denominator) + Stake
• Implied Probability: denominator / (numerator + denominator)

Examples: 

• 5/1: A CA$10 bet at 5/1 returns CA$60 in total (profit CA$50 + stake CA$10).

Implied Probability: 1 / (5 + 1) = 1/6 ≈ 16.67% — the market is pricing about a one-in-six chance.

• 4/7: A CA$70 bet returns CA$110 in total (profit CA$40 + stake CA$70). 

Implied Probability: 7 / (4 + 7) = 7/11 ≈ 63.64% — an odds-on favourite priced to win a little under two-thirds of the time.

Note: “Odds-on” means the denominator is larger than the numerator (e.g., 4/7). That implies a greater than 50% chance and a profit smaller than your stake. The opposite is “odds-against” (e.g., 5/1), where profit exceeds the stake.

Fractional odds are most common in horse racing and soccer competitions in the UK and Ireland, but you’ll see them in other markets like the Champions League, Premier League, Ligue 1, La Liga, Nations League, and domestic cups.

Decimal Odds (European Format): The Simplest to Use

Decimal odds show your total return per unit staked. Many bettors prefer this format because you can read the full return at a glance.

• Payout: Stake × Decimal
• Profit: Stake × (Decimal − 1)
• Implied Probability: 1 / Decimal

Examples:

• 2.00: A CA$10 bet returns a total of CA$20 (profit: CA$10). 

Implied Probability: 1 / 2.00 = 0.50 = 50% — essentially an even coin-flip price.

• 1.65: A CA$10 bet returns a total of CA$16.50 (profit: CA$6.50). 

Implied Probability: 1 / 1.65 ≈ 0.6061 = 60.61% — priced a bit over three wins in five.

Decimal odds work especially well in live markets and fast-paced games such as NBA quarters, NHL periods, UFC rounds, MLB innings, and in-play soccer. 

American Odds (Moneyline Format): Plus vs Minus

American (moneyline) odds use plus (+) signs for underdogs and minus (−) signs for favourites. Once you understand plus and minus, you’ll be able to read sports betting lines quickly.

+ or − in betting:

• +150 means that you risk 100 to win 150 (underdog). You’re backing the less likely outcome, so the book pays more if it lands. Your total return includes both profit and your stake.
• −120 means that you risk 120 to win 100 (favourite). You’re paying extra because the outcome is more likely. If it wins, you get your profit and your original stake.

Implied Probability:

• For +A: 100 / (A + 100). This converts a plus price into the chance the book is pricing in. For +150, it’s 100/250 = 40%, meaning the market suggests this wins four times out of 10.
• For −B: B / (B + 100). This converts a minus price into an implied chance. For −120, it’s 120/220 ≈ 54.55%, so the favourite is priced a little better than a coin flip.

Examples: +150 (underdog), −120 (favourite)

• +150: CA$100 wins CA$150 (total return CA$250). Bigger upside and lower winning odds.
• −120: CA$120 wins CA$100 (total return CA$220). Lower upside and higher chance to cash.

Moneyline is standard across the NFL, NBA, NHL, MLB, NCAA, CFL, UFC, and many other North American markets.

Odds Format Comparison: Which One Should You Use?

Pick the odds system that helps you decide quickly and avoid mistakes. Decimal is the simplest for reading total returns. American is standard in North America and pairs well with “favourite vs. underdog” thinking. Fractional odds work best for each-way horse racing and some soccer futures.

Table: Fractional vs. Decimal vs. American

Here’s a quick side-by-side view to help you choose the odds system that matches how you think. Focus on two things as you scan it: how fast you can read total return, and how easily you can see the implied chance. If you bet live or switch sports often, pick the format that minimizes your mistakes.

Use the table as a rule of thumb: 

• If you want to see an instant total return, use decimal odds. 
• If you’re into North American markets and want a quick favourite vs. underdog read, moneyline (American) will feel natural. 
• If you bet on racing or soccer cups and think in profit-to-stake terms, fractional works best. 

Whatever you choose, stick to one display on your slip, convert prices when you compare books, and always check implied probability before you bet.

How to Convert Odds Between Formats

Use these quick rules (or an online calculator) to compare betting odds across books and markets and spot bad odds quickly:

• Fractional → Decimal: 

Decimal = (num/denom) + 1 

Example: 5/1 → (5/1) + 1 = 6.00 

4/7 → (4/7) + 1 ≈ 1.5714

• Decimal → Fractional: 

Fractional = (Decimal − 1), simplified (e.g., 1.65 → 13/20)

Example: 1.65 → 0.65 = 65/100 = 13/20 

2.40 → 1.40 = 140/100 = 7/5 (after simplification)

• American (+A) → Decimal: 

Decimal = 1 + (A / 100) 

Example: +150 → 1 + 1.50 = 2.50

+130 → 1 + 1.30 = 2.30

• American (−B) → Decimal:

Decimal = 1 + (100 / B)

Example: −120 → 1 + (100/120) = 1.8333

−175 → 1 + (100/175) ≈ 1.5714

Decimal → American:

• If Decimal ≥ 2.00: +[100 × (Decimal − 1)] 

Example: 2.25 → +100 × 1.25 = +125

3.60 → +100 × 2.60 = +260

• If Decimal < 2.00: −[100 / (Decimal − 1)] 

Example: 1.91 → −[100 / 0.91] = −109.89 → −110 (rounded) 

1.65 → −[100 / 0.65] = −153.85 → −154 or −155 depending on the book’s rounding.

Rounding tip: American odds are typically rounded to the nearest 5 or 10 tick (e.g., −109.9 → −110; −153.8 → −154 or −155).

Common Mistakes to Avoid When Reading Odds

• Confusing profit with total return. Decimal odds include your stake; fractional and American examples above show profit figures.
• Ignoring implied probability. Convert the price into a percentage chance to check if the number makes sense in the context of the match, league, or playoffs (finals pressure, travel, injuries).
• Forgetting the vig. Books build a margin into their prices, meaning that two sides won’t sum to 100%.
• Mixing formats mid-bet. Stick to one format on your slip so your brain processes the numbers consistently.
• Chasing live swings without context. In-play odds shift quickly — make sure you know the game state (power play in the NHL, red card in soccer, late game in the NBA) before you click.
• Assuming “bigger number = better bet.” Big plus prices often reflect low probabilities. Value lives where your estimate beats the market, not where the payout looks flashy.
• Not using tools. Use a simple odds calculator to compare lines and make sure you actually understand the bet before staking.

Final check: Convert the line, compare across books, and only bet when you fully understand the betting odds.

Final Thoughts

Odds in betting are simply price tags on outcomes. Choose one format, learn the math, and stick with it.

When comparing books, convert formats to the same yardstick and note the margin (overround) so you’re judging the true price, not the packaging. 

If you can explain a line’s chance in plain percentage and show its equivalent in another format, you’re ready to make cleaner, higher-quality decisions.

Responsible Gambling

Stay in control with a few rules you can follow every time you bet:

• Set a budget and stick to it. 
• Cap your stake size per bet and per session. 
• Schedule breaks — step away if you feel tired or tilted. 
• If the odds look off or you don’t fully understand them, pass. 
• Keep balance: gambling should fit around life and work, not the other way around.

Safeguards worth using: enable deposit limits, reality checks (timed pop-ups), time-outs, and self-exclusion in your account menu.

If it stops being fun, talk to someone. Help is free, confidential, and available 24/7:

• Ontario: ConnexOntario — chat/phone referrals to problem-gambling services: 1-866-531-2600. 
• British Columbia: Gambling Support BC — counselling, information, and self-assessment tools: 1-888-795-6111.
• Alberta: Alberta Health Services Addiction Helpline — 1-866-332-2322 (province-wide). 
• Québec: Gambling: Help and Referral — 1-800-461-0140 (bilingual, 24/7). 
• Pan-Canadian: Responsible Gambling Council — “Help for Canadians” and treatment centre locator. 

Prefer chatting first? Most provincial services offer live chat in addition to phone lines (see the sites above for options).