Enter the odds for every outcome of a market — 2 for tennis or totals, 3 for football 1X2, more for outrights. See the overround you're paying and what fair odds would look like with the margin stripped out.
Worked example — typical football 1X2 at 2.45 / 3.30 / 3.10: implied 40.8% + 30.3% + 32.3% = 103.4% book → 3.4% margin. Fair odds: 2.53 / 3.41 / 3.20.
Margin varies far more than most bettors realise — between bookmakers, between markets at the same bookmaker, and between main lines and props. Beating a 3% margin is twice as easy as beating 6%. If you take one habit from this page: check the margin on the markets you actually bet, and move your action to where it's lowest. It's the only edge that requires zero prediction skill.
2–3% at sharp books on big markets, 4–7% mainstream football/tennis, 8%+ on props and niche markets. Acca legs compound: five 5%-margin legs ≈ 28% total.
Same concept — expected payout per unit staked across the whole market. Unlike slots, in sports betting your selection skill moves your personal RTP above or below the market's.
It's the standard first approximation. Real margins skew toward longshots (favourite-longshot bias), so fair odds on favourites are slightly better than proportional, on outsiders slightly worse.
The market's payout is theory; your own is fact. Zort tracks every bet you place and shows your actual return per bookmaker and market type — usually a sobering read, always a useful one.
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