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Bookmaker odds look like a simple multiplier, but behind every number is pricing with a built-in bookmaker's margin. If you understand how the rate is formed and how to extract the implied probability and margin from it, you can compare the two bids and avoid matches where the office holds too much margin. This article goes through the basics of decimal odds, calculating the margin (overround), the differences between sports, the Asian Handicap, stacked margin for accumulators and a peak at value betting, the Kelly stake and CLV (closing line value).
Decimal rate: what exactly it says
The decimal odds (the European format, the one you see in all Ireland bookies) tells you how many times your stake will be won if you win - including the stake itself. Odds of 2.50 means: for a bet of β¬10 you will be paid β¬20 (= 250 Γ 2.50), the net profit is β¬10.
| Course format | Example | What does he say? | With a bet of β¬10 |
|---|---|---|---|
| Decimal (European) | 2.50 | Amount paid out= deposit x exchange rate | β¬20 paid |
| Fractional (British) | 3/2 | Net Profit= Deposit Γ (3/2) | β¬20 paid |
| American (Moneyline) | +150 | Profit from bet 100 | β¬20 paid |
In Ireland offices (Tipsport, Fortuna, Sazka, Chance, SYNOT TIP, Forbet, Betano, Maxa) you will only encounter a decimal rate.
Implied probability
The odds can be used to determine the probability the office gives to a given outcome. Formula:
Implied probability= 1 Γ· odds Γ 100%
- Odds 1.50 β 1 Γ· 1.50= 66.67% probability
- Odds 2.00 β 1 Γ· 2.00= 50% probability
- Odds 3.00 β 1 Γ· 3.00= 33.33% probability
- Odds 5.00 β 1 Γ· 5.00= 20% probability
- Odds 10.00 β 1 Γ· 10.00= 10% probability
Note: the implied probability is not the pure probability - it includes the office margin. The office's true estimate (its "fair" rate) is higher than the implied probability indicates. The difference is precisely the margin.
Margin (overround) and its calculation
The office margin (overround) is the sum of the implied probabilities of all possible outcomes of the match minus 100%. Formula:
Margin= (sum of implied probabilities of all outcomes) β 100%
Example football 1X2: odds 2.10 (home)/3.40 (draw)/3.60 (away).
- Implied home probability: 1 Γ· 2.10= 47.62%
- Implied probability of a draw: 1 Γ· 3.40= 29.41%
- Implied away probability: 1 Γ· 3.60= 27.78%
- Sum: 47.62 + 29.41 + 27.78= 104.81%
- Margin: 104.81 β 100= 4.81%
Example tennis (two-way bet, no tie): odds 1.90/1.90.
- (1 Γ· 1.90 + 1 Γ· 1.90) Γ 100= 52.63 + 52.63= 105.26%
- Margin: 5.26%
A sensible player calculates the margin before each bet (or uses a calculator). 1.90/1.90 odds are fairer than 1.85/1.85 (8.11% margin) despite the seemingly small difference.
Reasonable margin according to sport and bet type
| Sports/market | A fair margin | Expensive margin | Note |
|---|---|---|---|
| Major European Football Leagues (1X2) | 4-6% | above 8% | Premier League, La Liga, Bundesliga, Serie A |
| League of Ireland (1X2) | 5-7% | above 9% | Less strike volume= higher margin |
| Hockey extra league (1X2) | 6-8% | above 10% | Ireland bookmakers have a slightly higher margin here |
| NHL (1X2) | 5-7% | above 9% | An international league with high liquidity |
| Tennis ATP/WTA (two-way) | 5-7% | above 8% | The Grand Slam has the lowest margin |
| Asian Handicap (major leagues) | 2-3% | above 5% | The most advantageous type of bet mathematically |
| Number of goals under/over | 4-6% | above 8% | The second most advantageous type of bet |
| Accurate result | 15-20% | above 25% | High margin, many options |
| First shooter | 10-15% | over 20% | Special market, marketing attractive |
| Live Betting (Major Markets) | 8-12% | above 14% | Higher margins due to player emotion and speed |
Veteran rule: If the margin exceeds 8-10% on the main market, skip the bet or look for the same match in another office. A difference of 2 percentage points of the margin means a long-term difference in the result of 200 β β¬ 20 per 100 bets of β¬ 10. Detail in value betting .
βοΈ Comparison of Ireland office margins
Margins differ between Czech offices depending on the volume of bets and trading strategy. The values ββbelow are indicative (season 2026/25) and always check in specific matches. The market detail is changing rapidly:
| Office | Main football 1X2 | Hockey 1X2 | Tennis ATP/WTA | Asian Handicap |
|---|---|---|---|---|
| Tipsport | 5-7% | 6-8% | 5-7% | 2-4% |
| Fortuna | 5-7% | 6-8% | 5-7% | 2-4% |
| Bet | 6-8% | 7-9% | 6-8% | 3-5% |
| SYNOT TIP | 6-8% | 7-9% | 6-8% | 3-5% |
| Chance | 6-8% | 7-9% | 6-8% | 3-5% |
| Forbet | 6-8% | 7-9% | 6-8% | 3-5% |
| Max | 7-9% | 8-10% | 7-9% | 4-6% |
| Beta | 6-8% | 7-9% | 6-8% | 3-5% |
Tipsport and Fortuna hold the lowest margins for a long time due to the largest volume of bets on the Ireland market. When betting on a mainstream European football match, it pays to compare the odds between Tipsport, Fortuna and e.g. Betan - with a margin of 5% vs 8%, the difference in payout is β¬30 - β¬2 per β¬ bet.
The Asian handicap and why it has a lower margin
The Asian Handicap removes the draw from the match β giving the favorite a goal weight (eg β1.5 goals) and the underdog a plus, so both sides finish at around 1.90 odds. The margin is lower (typically 2-3% per major league) for three reasons:
- The bet is mathematically two-way β easier calibration of the odds
- A popular type of bet among experienced players - the office cannot afford worse odds here
- Quarter handicaps (β0.25, β0.75) allow for "half win"/"half lose" - reduce swing in results
| Handicap | Importance | Example: home favorite β0.5 |
|---|---|---|
| β0.5 | The home team must win | Home wins β win; draw/lose β lose bet |
| -1.0 | Home team must win min. by 2 goals (otherwise deposit refund if you win by 1) | Wins 2:0 β win; 1:0 β return; draw/lose β lose |
| -1.5 | Home team must win min. by 2 goals | Wins 2:0 β win; 1:0 β loss; draw β loss |
| β0.25 | Half bet at β0, half at β0.5 | Draw β half returned, half lost; win β full win |
| β0.75 | Half bet on β0.5, half on β1.0 | Win by 1 β half win, half return; win by 2+ β full win |
For value betting, the Asian handicap is almost always more advantageous than the classic 1X2 - same match, lower margins, easier pricing.
Accumulator and folded margin
In the case of an accumulator (combination), the margin is not added, but multiplied. Formula:
The resulting accumulator margin= (1 + margin)^n β 1, where n is the number of bets and the margin is expressed as a decimal number.
| Number of bets | Margin 4% | Margin 6% | Margin 8% | Margin 10% |
|---|---|---|---|---|
| 1 | 4.0% | 6.0% | 8.0% | 10.0% |
| 2 | 8.2% | 12.4% | 16.6% | 21.0% |
| 3 | 12.5% | 19.1% | 26.0% | 33.1% |
| 5 | 21.7% | 33.8% | 46.9% | 61.1% |
| 10 | 48.0% | 79.1% | 115.9% | 159.4% |
The compound margin shows why accumulators are mathematically the least advantageous format. Therefore, offices often advertise accumulator bonuses of 10-50% - but even these bonuses do not compensate for the entire compounded margin. For long-term value betting, only single bets or double combinations are reasonable.
Value Bet and Expected Value (EV)
A value bet is created when the bookmaker's rate is higher than your estimated fair rate. Procedure:
- Estimate your own probability of the result as a percentage (based on form, stats, xG, injuries)
- Calculate the fair odds: fair odds= 1 Γ· your odds
- Compare with the office rate: if the office rate is higher than fair, you have value
- For a more accurate evaluation, use EV: EV= (odds Γ your probability) β 1
Example: You estimate the probability of team A winning at 45%. Fair odds= 1 Γ· 0.45= 2.22. The office offers 2.50. You have value. EV= (2.50 Γ 0.45) β 1= 0.125= +12.5%. Long-term profit on the bet.
The value betting trap: Without an objective model, it's easy to overestimate yourself. If you estimate the probability "by eye", your estimate is probably optimistic. Start with a 1% fixed bet bankroll and compare CLV (closing line value) after 100 bets - that alone is hard proof of advantage.
Kelly's deposit calculation
Kelly's calculation (Kelly's criterion) is a mathematical formula for the optimal bet size at a proven advantage:
F= (k Γ p β 1) Γ· (k β 1)
Where f= recommended bankroll fraction, k= decimal odds, p= Your estimated probability of winning
Example: Odds 2.50, Your probability 45%. F= (2.50 Γ 0.45 β 1) Γ· (2.50 β 1)= 0.125 Γ· 1.50= 0.0833= 8.33% of bankroll. With a β¬1 bankroll, that would be β¬ per bet.
Full Kelly is very aggressive - leading to high drawdowns when overestimating the probability. Experienced players therefore bet:
- Half Kelly: 4.17% of bankroll= β¬20
- Quarter Kelly: 2.08% of bankroll= β¬10
Without the model's own probability estimates, Kelly is useless. Fixed bankroll percentages (1-2%) are safer for a beginner.
Closing rate and CLV (closing line value)
The closing price is the last price just before kick-off - the most accurate estimate of the result that the market will achieve (after including all new information: lineups, weather, late bets).
CLV (closing line value) measures whether your bets were placed at a better rate than the closing rate. If you long-term bet on odds of 2.50 and the closing average is 2.40, you have a CLV of +4.2%. This is a harder proof of advantage than a short-term win balance:
- Positive CLV= the market is right, you have an advantage
- Neutral CLV (0%)= you play around randomness
- Negative CLV= short term gain was just luck, long term you will lose
Practical implication: If you have +20% balance but -3% CLV for 50 bets, your results are the result of luck, not skill. After another 100 bets, the market will "catch up" with you and the balance will drop to a negative expectation. That's why professional punters track CLV as a primary metric.
β‘ Live odds: higher margins and model errors
Live odds have a higher margin for two reasons:
- The office has less time to precisely calibrate the rates and insures itself with a higher margin against a possible model error
- Players in live mode bet more emotionally and do not calculate the margin - the office knows this
Typical difference: pre-match 5-8% margin, live 8-12% on main bets and 15% and more on special markets. Detail in cashout and live betting explained .
Related articles:
- Value betting and the Kelly criterion
- Cashout and live betting explained
- Budget management in an online casino
- Betting systems in roulette
- Hockey live stream
- Football live stream
β Frequently asked questions about rates and margin
Value betting Cashout and live bets
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