Implied Probability Explained

The formula: turning decimal odds into a percentage

South African books mostly display decimal odds, which makes the maths quick.

Implied probability (%) = (1 ÷ decimal odds) × 100

• 1.50 → 1 ÷ 1.50 = 0.667 → 66.7%
• 2.00 → 1 ÷ 2.00 = 0.500 → 50.0%
• 3.40 → 1 ÷ 3.40 = 0.294 → 29.4%
• 6.00 → 1 ÷ 6.00 = 0.167 → 16.7%
• 11.00 → 1 ÷ 11.00 = 0.091 → 9.1%

The shorter the price, the higher the implied chance. A 1.20 favourite is being priced at roughly an 83% chance; a 15.00 outsider at about 6.7%. Reverse it and you can turn your own opinion into a price: if you think a side has a 40% chance, the fair odds are 1 ÷ 0.40 = 2.50. Anything longer than 2.50 on that selection is, by your read, value.

Why the percentages add up to more than 100%

Add the implied probabilities of every outcome in a market and you will not get 100%. You will get more — usually somewhere between 104% and 110% on a three-way football match. That extra chunk is the bookmaker margin (also called the overround or vig), and it is how the book builds in its edge regardless of who wins.

Worked example — a Premiership (PSL) match priced three ways:

• Home win 2.10 → 1 ÷ 2.10 = 47.6%
• Draw 3.30 → 1 ÷ 3.30 = 30.3%
• Away win 3.75 → 1 ÷ 3.75 = 26.7%

Total = 47.6 + 30.3 + 26.7 = 104.6%

That 4.6% over 100 is the margin on this market. To find each outcome's true (margin-free) probability, divide each implied figure by the total:

• Home: 47.6 ÷ 104.6 = 45.5%
• Draw: 30.3 ÷ 104.6 = 29.0%
• Away: 26.7 ÷ 104.6 = 25.5%

Now the three add to 100%. The book is quietly telling you the home side is a genuine 45.5% shot, but it is only paying you as if it were 47.6% — the gap is the house cut.

Margin varies by bookmaker — and that changes your price

The lower a bookmaker's margin, the closer its odds sit to the true probability, and the more the payout stays in your pocket. Across the football markets we sample, average margins differ noticeably between South African books.

From our sampled odds data:

• 10bet — average margin about 4.8% (sample of 27 markets), and it held the best available price in roughly 85% of those markets.
• Betway — average margin about 6.5% (sample of 238 markets), best price share around 91%.
• Sportingbet — average margin about 8.6% (sample of 39 markets), best price share around 28%.

Sample sizes vary a lot here, so treat the smaller samples cautiously. The pattern still matters: a market priced at a 4.8% overround gives you a better implied chance-to-price ratio than the same market at 8.6%. On a single bet that difference looks small; across a season of stakes it is the difference between a leaky and a tight betting record. This is exactly why comparing the same fixture across books before you stake is worth the two minutes.

Using implied probability to find value

Value exists when your estimated probability of an outcome is higher than the implied probability in the odds. The method is simple:

1. Convert the odds to implied probability. 2. Strip out the margin to get the true implied probability (as shown above). 3. Compare that against your own honest estimate.

Say a bookmaker prices Stormers to beat a touring side at 2.40. That implies 1 ÷ 2.40 = 41.7%. If you strip a typical margin and you still rate the Stormers at, say, 50% based on form, home advantage and team news, the price is generous — the book is under-rating them relative to your read, and there is value.

The discipline is being honest about your own number. Most bettors overrate their favourites. A quick sanity check: if your estimate is wildly different from the margin-free market number, ask what you know that the market doesn't. Often the answer is nothing, and the market is right.

You can cross-check your read against our published predictions and market movers, which track where prices are drifting or shortening ahead of kick-off.

Quick reference table for common decimal odds

Keep this handy for rugby, cricket, tennis and football markets:

• 1.20 → 83.3%
• 1.40 → 71.4%
• 1.50 → 66.7%
• 1.80 → 55.6%
• 2.00 → 50.0%
• 2.50 → 40.0%
• 3.00 → 33.3%
• 4.00 → 25.0%
• 5.00 → 20.0%
• 6.00 → 16.7%
• 10.00 → 10.0%
• 21.00 → 4.8%

For two-way markets — a tennis match, an MMA / UFC fight, or a cricket match with no draw priced — the two implied probabilities should add to just over 100%. On a UFC bout priced 1.55 (64.5%) and 2.50 (40.0%), the total is 104.5%, so the margin is 4.5% and the fighters' true chances are roughly 61.7% and 38.3%.

Where implied probability fits into match-day decisions

Implied probability is the bridge between a fixture list and a staking decision. Before you back anything:

• Convert the price to a percentage so you know what the market is actually claiming.
• Compare the same selection across two or three books to see who is offering the lowest margin and best price.
• Only stake when your number beats the margin-free market number.

For accumulators, multiply the implied probabilities together: a four-fold of legs at 1.80, 1.90, 2.10 and 1.65 has a combined true chance far lower than any single leg feels — which is why long multis are hard to land even when each pick looks sensible. Each added leg stacks another slice of margin on top, too.

Use our betting odds pages and comparison tools to line up prices on today's matches, then apply the formula before you commit a stake.