Implied probability is the single most useful idea in sports predictions. It translates a price into a percentage chance. Once you can do that, you stop thinking "this team is a big favorite" and start thinking "the market says this team wins 70% of the time. Do I agree?"
What implied probability means
Every price has a probability baked into it. If a price pays you exactly enough to break even over the long run at a 40% win rate, its implied probability is 40%.
It is called "implied" because the odds do not state it directly. You have to calculate it.
The formulas
Decimal odds Implied probability = 1 ÷ decimal odds
- 2.50 → 1 ÷ 2.50 = 40%
American odds, minus Implied probability = odds ÷ (odds + 100)
- -150 → 150 ÷ 250 = 60%
American odds, plus Implied probability = 100 ÷ (odds + 100)
- +200 → 100 ÷ 300 = 33.3%
Fractional odds Implied probability = bottom ÷ (top + bottom)
- 3/1 → 1 ÷ 4 = 25%
A full worked example
An NBA game is listed:
- Home: -180
- Away: +155
Home implied probability: 180 ÷ 280 = 64.3% Away implied probability: 100 ÷ 255 = 39.2%
Add them: 64.3% + 39.2% = 103.5%
That is more than 100%, which is impossible for real probabilities. The extra 3.5% is the house margin (the vig). The prices are slightly worse than fair on both sides.
Removing the vig to find "fair" probability
To estimate what the market really thinks, divide each side by the total:
- Home: 64.3 ÷ 103.5 = 62.1%
- Away: 39.2 ÷ 103.5 = 37.9%
Now they add up to 100%. These are often called no-vig or fair probabilities. This simple method is good enough for most purposes. (More advanced methods adjust favorites and underdogs differently, but the difference is usually small.)
Using implied probability to judge a price
Here is the practical use. Suppose you have done your homework and believe the away team actually wins 42% of the time.
- Market's implied chance at +155: 39.2%
- Your estimate: 42%
Your estimate is higher than the price implies, so by your numbers the away team is underpriced. That is the definition of a value bet.
Let's check with expected value. Imagine 100 identical picks of 100 each at +155:
- You win 42 times × 155 profit = 6,510
- You lose 58 times × 100 = 5,800
- Net = +710, or about +7.1 per pick
If instead your honest estimate were 36%:
- 36 × 155 = 5,580
- 64 × 100 = 6,400
- Net = -820
The price did not change. Only your probability estimate did. That is why the skill that matters is estimating probability better than the market, not picking winners.
Break-even win rates
Implied probability is also your break-even rate. To profit at a given price, you must win more often than its implied probability.
| Price | Break-even win rate | |---|---| | -200 | 66.7% | | -110 | 52.4% | | +100 | 50.0% | | +150 | 40.0% | | +300 | 25.0% |
The -110 line is worth memorizing. At standard spread and total prices you need to win 52.4% of your picks just to break even. Many people are surprised by how hard that is.
Implied probability in three-way markets
In soccer, there are three outcomes: home, draw and away.
- Home 2.20 → 45.5%
- Draw 3.30 → 30.3%
- Away 3.40 → 29.4%
- Total → 105.2%
Fair probabilities after removing the margin: 43.3%, 28.8%, 28.0%. Draws are common in soccer, and implied probability makes that clear. See soccer 3-way odds.
Implied probability for futures
Championship markets have many outcomes, so the margins add up. If you add the implied probabilities of every team in a futures market, you may get 120% to 140%. That means individual futures prices are usually further from fair than single-game prices. Our guide to championship odds covers this.
Common mistakes
- Treating implied probability as truth. It is the market's estimate plus a margin, not a fact.
- Forgetting the vig. Always remember the raw numbers add up to more than 100%.
- Confusing likely with good value. A 75% favorite can still be a bad price if it really wins only 70% of the time.
Practice it on real lines
A good habit: before every pick, write down the implied probability and your own estimate. On MockSport you can make free play-money picks on real lines, then look back at your history to see whether your estimates were too high or too low. Start with today's odds.
FAQ
Why do implied probabilities add up to more than 100%?
Because each price includes a margin for the house. The amount over 100% is called the overround or vig. Dividing each side by the total gives fair probabilities.
What is the implied probability of -110?
110 ÷ 210 = 52.4%. That is also the win rate you need to break even when picking at -110.
Is implied probability the same as the real chance of winning?
No. It is the market's estimate including a margin. Markets are often accurate, but they are not perfect, which is why people look for prices that differ from their own estimates.