What POP actually measures
Probability of profit answers one question: what are the odds this trade makes money if held to expiration? It is derived from the option's pricing model, which converts the current stock price, strike, time left, and implied volatility into a probability distribution of expiry prices. POP is the share of that distribution landing in your profit zone. A 75% POP means the model expects roughly 3 wins in 4 identical trades, not that this trade is safe.
The delta shortcut
Delta doubles as a rough probability gauge. A 0.25-delta put has about a 25% chance of expiring in the money, so a short put at that delta has about a 75% chance of expiring worthless, which is exactly when the seller keeps the premium. Hence the shortcut: POP ≈ 1 - delta for short puts, and POP ≈ delta for long calls (the buyer needs the stock above the strike, then past the premium).
Worked example: selling a put at 75% POP
You sell a $95 strike put for $1.50 per share when its delta is 0.25. Premium collected: $1.50 x 100 = $150, your maximum profit. Breakeven: $95 - $1.50 = $93.50. POP: roughly 1 - 0.25 = 75%, the model's estimate that the stock stays above $93.50 at expiry. The trade wins often and small: 75% odds of keeping $150, with the tail risk of the stock collapsing far below $95, where losses grow toward $9,350 at zero.
Why sellers usually show higher POP than buyers
Compare the short put above with buying a $50 strike call for $2.00 at 0.45 delta. The buyer's POP is roughly 45%, and the stock must clear the $52 breakeven, not just the $50 strike. The seller's edge is structural: they collect premium up front and win across a wider range of outcomes, including the stock doing nothing. The buyer's compensation is the payoff shape: uncapped gains when the rare big move lands. High POP with capped gains versus low POP with open-ended gains is the fundamental trade in options.
POP and expected value: the number that actually matters
A high POP can still be a bad trade. Take the short put: 75% POP, $150 maximum gain. Expected value = (0.75 x $150) - (0.25 x average loss). For the trade to break even on average, the average loss must be exactly $450, because 0.75 x 150 = $112.50 and $112.50 / 0.25 = $450.
Now suppose the 25% tail averages a $1,000 loss when the stock collapses. Expected value = $112.50 - $250 = -$137.50 per trade. You win three times out of four and still lose money over time. This is the classic short-volatility trap: frequent small wins funding rare large losses. Always pair POP with the max-loss math. A 45% POP buyer risking $600 to make $2,400 breaks even at just a 20% win rate (600 / (2,400 + 600) = 20%), so the lower-POP trade can carry the better expected value.
What POP leaves out
POP says nothing about how much you win or lose. A trade with 90% POP collecting $0.10 per share risks a 10% tail that can dwarf the frequent small wins; that is the classic short-volatility blowup. POP is also a snapshot: it moves as the stock moves and as volatility changes, and it assumes the model's distribution, which underestimates real-world crashes. Use POP to size positions and set expectations, never as a reason to skip the max-loss math on our calculator.