Expected Value (EV)

The average return per unit staked on a bet, given your estimated probability and the offered odds. Positive EV means the bet is profitable on average.

Expected value (EV) is the average return per unit staked, computed from your estimated win probability p and the decimal odds O:

EV = p × O − 1

EV is in units of stake. EV = +0.30 means a £1 bet returns £1.30 on average over many repetitions (£0.30 profit). EV = −0.05 means it loses 5p per £1 on average.

Why EV alone isn't enough:

  • EV doesn't tell you about variance. A +5% EV bet at price 50.0 is a roulette wheel; the same +5% at price 1.5 is steady. Use Kelly to size stake to the price profile.
  • EV is only as good as your p. Overestimate p by 5pp and a "+30% EV" bet might really be +10% or negative.

The TrapStats EV pipeline:

  1. Model produces raw prob_win.
  2. Calibrator maps it to a calibrated probability.
  3. Shrinkage blends with market: pw_eff = (1−λ)·prob_win + λ·(1/price), λ=0.30.
  4. ev = pw_eff × price − 1.
  5. Gates: skip if ev < 0.25 (too marginal) or ev > 0.50 (implausibly high → model-overconfidence flag).
  6. Stake from EV-tier table (1%/2%/3% of bankroll).

The "Why this pick" panel on each pick shows all five steps explicitly.

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