Implied probability explained

The formula: decimal odds to a percentage

For decimal odds, implied probability = (1 ÷ 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%
• 5.00 → 1 ÷ 5.00 = 0.200 → 20.0%

The lower the odds, the higher the implied probability, because the market thinks the outcome is more likely. If you still bet in fractional odds — common on Irish racing cards — convert to decimal first. Fractional to decimal is (numerator ÷ denominator) + 1, so 6/4 = 1.5 + 1 = 2.50, which is 40% implied. 5/2 = 3.50, which is 28.6%.

That is the whole calculation. The harder, more useful part is understanding why the percentages on a full market never add up to a clean 100%.

Why the market's probabilities add up to more than 100%

Add up the implied probabilities across every outcome in a market and you get a number above 100%. That surplus is the bookmaker's margin — the built-in edge, sometimes called the overround or the vig.

Take a two-way market, say a tennis match on the ATP Tour priced 1.80 / 2.10:

• 1.80 → 55.6%
• 2.10 → 47.6%
• Total = 103.2%

The 3.2% above 100% is the margin. On a three-way football market (home / draw / away) the same principle stacks across three prices, which is why football overrounds are usually larger than clean two-way tennis or head-to-head markets.

This is where the odds_metrics in our operator data matter. Across sampled markets, Betfair shows the lowest average margin at roughly 4.3%, with Unibet near 5.7% and Ladbrokes around 5.8%. At the wider end, LiveScore Bet sits near 8.4% and BetVictor near 7.5%. A tighter margin means the posted probabilities sit closer to the true 100%, so you keep more of any edge you find.

Stripping out the margin: your true implied probability

To compare a price fairly against your own view, remove the margin. The quick method is to divide each outcome's raw implied probability by the market total.

Using the tennis example (55.6% and 47.6%, total 103.2%):

• Player A true probability: 55.6 ÷ 103.2 = 53.9%
• Player B true probability: 47.6 ÷ 103.2 = 46.1%
• These now sum to 100%

So the market's genuine read on Player A is closer to 53.9%, not the 55.6% the raw price implies. If your own analysis says Player A wins 60% of the time, you have a potential value bet — your estimate is meaningfully above both the raw and the margin-adjusted figure. If you think it is 50%, the price is against you and you pass.

This margin-adjusted number is the honest baseline. Comparing your estimate to the raw implied probability alone flatters the bet, because part of that raw figure is just the bookmaker's cut.

A worked example on a Premier League match

Say a Premier League fixture is priced up as:

• Home 2.30 → 43.5%
• Draw 3.40 → 29.4%
• Away 3.20 → 31.3%
• Total = 104.2% (a 4.2% margin)

Margin-adjusted true probabilities:

• Home: 43.5 ÷ 104.2 = 41.7%
• Draw: 29.4 ÷ 104.2 = 28.2%
• Away: 31.3 ÷ 104.2 = 30.0%

Now suppose your read of form, injuries and home advantage puts the home win at 48%. The market's honest number is 41.7%, so you rate the home side more likely than the price does — that is where value sits.

Expected value check on a €10 stake at 2.30: EV = (0.48 × €13.00 profit) − (0.52 × €10 stake) = €6.24 − €5.20 = +€1.04 per €10 staked. A positive figure means the bet is worth taking at that price and your estimate. Flip your estimate to 40% and the same sum turns negative, so the number you assign yourself is doing all the heavy lifting. Be honest with it.

Comparing prices to protect your edge

Any edge you find is only as good as the price you actually get on. Because margins differ by operator, the same outcome carries a different implied probability at different books. A shorter price means a higher implied probability and a smaller share of value handed to you.

Our sampled best-price share backs this up: Betfair topped the sample at roughly 53% of best prices, with Ladbrokes near 22%, William Hill and Unibet around 17%. Operators like BetVictor (about 6%) and LiveScore Bet (about 10%) led on the top price far less often in the sample.

The practical move is to line up the same market across a few Irish-facing books before you stake, especially on the fixtures where you already have a strong view. Even a move from 2.20 (45.5%) to 2.35 (42.6%) shifts the implied probability nearly three points in your favour, which over a season of bets is the difference between a positive and negative ledger.

Where implied probability fits into betting in Ireland

All the operators in our data hold a licence to operate for the Irish market, with Paddy Power, BoyleSports and Novibet noted under the Gambling Regulatory Authority of Ireland (GRAI). The minimum age to bet is 18. Standard minimum deposit across the listed books is €10, with withdrawals quoted in a 0–24h window and PayPal supported throughout; Apple Pay and Revolut Pay appear at a smaller group including bet365 and Paddy Power.

None of that changes the maths — a price is a price — but it does mean you can act on your calculation quickly on a match day and pull winnings without long delays. Use implied probability as your filter: work out the margin-adjusted true chance, set it against your own estimate, and only take prices where your number is clearly higher. Everything else on the coupon is noise.