Reading betting odds: implied probability and the bookmaker’s margin

Decimal odds and what they pay

Philippine sportsbooks usually show decimal odds. The number is your total return per ₱1 staked, including your stake. A ₱100 bet at 2.50 returns ₱250 if it wins: ₱150 profit plus your ₱100 back.

Implied probability

Divide 1 by the decimal odds to get the probability the price implies:

• 2.00 → 50%
• 2.50 → 40%
• 1.50 → about 66.7%

A bet only has positive value if you believe the real chance is higher than the implied one — and the bookmaker usually knows the market better than most bettors.

The margin built into every market

Add up the implied probabilities of all outcomes in a market. For a fair coin priced 1.90 on each side: 52.6% + 52.6% = 105.3%. The extra 5.3% is the bookmaker’s margin (overround). It means that over time bettors as a group get back roughly 95% of what they stake on that market. Lower margins are better for you; compare them between sportsbooks.

Why parlays cost more

In a parlay (accumulator) the odds multiply — and so do the margins. Four picks at 1.90 pay 1.90 × 1.90 × 1.90 × 1.90 ≈ 13.0, while the fair price for four 50% chances is 16.0. You are paid about 81% of a fair return instead of about 95% on a single bet. Big parlay payouts look attractive because the cost is hidden.

Other odds formats

• Fractional 3/2 = decimal 2.50.
• American +150 = decimal 2.50; American −200 = decimal 1.50.
• Hong Kong odds show profit only: HK 1.50 = decimal 2.50.

Whatever the format, convert to decimal and implied probability to compare prices fairly.