Implied probability explained

The formula: turning decimal odds into a percentage

Every price on a Betway, Hollywoodbets or Sportingbet coupon is a decimal number in South Africa. To get the implied probability, divide 1 by that number.

• Odds 1.40 → 1 ÷ 1.40 = 0.714 → 71.4%
• Odds 2.50 → 1 ÷ 2.50 = 0.400 → 40.0%
• Odds 4.00 → 1 ÷ 4.00 = 0.250 → 25.0%
• Odds 10.00 → 1 ÷ 10.00 = 0.100 → 10.0%

The shorter the odds, the higher the implied probability — the bookmaker rates that outcome as more likely. A big underdog at 10.00 carries only a 10% implied chance.

To reverse it, divide 1 by your probability (as a decimal): a 40% chance is fair at 1 ÷ 0.40 = 2.50. This reverse step is how you work out whether a posted price is generous or mean compared to what you think will happen.

Worked example: a PSL match on the coupon

Say a Premiership (PSL) fixture is priced like this:

• Home win: 2.10
• Draw: 3.30
• Away win: 3.80

Convert each price:

• Home: 1 ÷ 2.10 = 0.476 → 47.6%
• Draw: 1 ÷ 3.30 = 0.303 → 30.3%
• Away: 1 ÷ 3.80 = 0.263 → 26.3%

Add them: 47.6 + 30.3 + 26.3 = 104.2%.

A true probability set for one match should total 100%. The extra 4.2% is the bookmaker's margin — sometimes called the overround or the vig. It is how the operator builds in its edge across all three outcomes. Every fair-looking market is inflated this way, which is why raw implied probabilities always slightly overstate each outcome's real chance.

Removing the margin for a fair probability

The raw percentages above are not the bookmaker's genuine view — they're padded. To get closer to a fair estimate, divide each raw probability by the total (104.2%, or 1.042 as a decimal):

• Home: 47.6 ÷ 104.2 = 45.7%
• Draw: 30.3 ÷ 104.2 = 29.1%
• Away: 26.3 ÷ 104.2 = 25.2%

Now they add to 100%. These normalised figures are the closest simple estimate of the operator's true opinion, with the margin stripped out.

This matters when you are hunting value. If you rate the away side's chance at 30% but the fair implied probability is only 25.2%, the price may be worth backing — your estimate is higher than the market's. If you rate it at 20%, the bet is poor value even though 3.80 looks tempting.

The margin varies by operator — and it's a real cost

The bookmaker margin is a genuine cost that eats into long-term returns. Across a sample of football markets in our odds data, average margins differed by operator:

• 10bet: about 4.8% average margin (sampled 27 markets)
• Betway: about 6.5% average margin (sampled 238 markets)
• Sportingbet: about 8.6% average margin (sampled 39 markets)

A lower margin means the implied probabilities are less inflated and the prices are, on average, closer to fair. On the same sample, Betway offered the best available price in roughly 91% of markets checked, 10bet in about 85%, and Sportingbet in about 28%. Sample sizes differ, so treat the smaller samples as indicative rather than definitive.

Editorial view: if you care about squeezing value from implied probability, tighter margins are the operators to lean on — Betway and 10bet come out well on the data above. You can compare live prices on our [betting odds South Africa](/en-za/odds/) pages before you commit.

Using implied probability to spot value bets

Value exists when your own estimate of a probability is higher than the fair implied probability behind the price. The workflow:

1. Take the decimal odds and convert to implied probability (1 ÷ odds). 2. Normalise across the market to remove the margin. 3. Compare the fair figure to your own honest estimate. 4. Back it only when your estimate is clearly higher — not marginally, because the margin and your own uncertainty both work against you.

Worked value check: a tennis outsider on the ATP Tour is priced 3.00 (33.3% raw). After normalising the market, the fair implied probability comes out at 30%. If your research suggests a genuine 38% chance, that gap is your edge. If you can only justify 30% or less, walk away.

This is exactly the logic behind our [predictions](/en-za/predictions/) and [market movers](/en-za/market-movers/) pages, where price shifts change the implied probability in real time.

Quick reference: common decimal odds and their implied probability

• 1.20 → 83.3%
• 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%

Keep this handy when scanning a coupon. If a price looks longer than the outcome deserves, the implied probability is low and the potential value is high — provided your own read is sound. Our [betting tools](/en-za/betting-tools/) section can help you run these conversions faster across multiple selections.