The Kelly criterion computes the bankroll fraction that maximises long-term growth when you have an edge: stake = edge ÷ (decimal odds − 1). Bigger edges justify bigger stakes; longer odds justify smaller ones at the same edge, because the win happens less often and variance is higher. Full Kelly is aggressive — most practitioners use a half or quarter Kelly to smooth the swings.
Beyond staking, Kelly is an excellent ranking metric. Raw edge percentage flatters longshots: a 30% 'edge' on a 21.00 outsider is usually a pricing artefact, not an opportunity. Dividing the edge by (odds − 1) weights value by how often it actually lands, which is precisely how our screener orders its picks — a modest edge on a 1.80 favourite can outrank a large edge on a 6.00 shot.
Edge 8% at odds 3.60: Kelly fraction = 0.08 / 2.60 ≈ 3.1% of bankroll. The same 8% edge at odds 1.60 gives 0.08 / 0.60 ≈ 13.3% — the shorter price justifies a much larger stake.