Delta as a probability proxy
Delta measures how much an option's price changes per $1 move in the underlying. A 0.30 delta put moves $0.30 for every $1 the stock drops. As a convenient shortcut, delta also approximates the probability of expiring in the money — a 0.30 delta put has roughly a 30% chance of being ITM at expiration. Premium sellers use this to quickly pick strikes: selling at 0.20 delta targets roughly 80% probability of the option expiring worthless.
Probability of Profit is more precise
POP measures something slightly different: the probability of a trade being profitable at expiration, not just whether a single option expires ITM. For a naked short put, POP ≈ 1 − delta, so they are nearly identical. But for credit spreads, POP accounts for the net credit received — your breakeven is not at the short strike but at the short strike minus the premium collected. This means POP is typically higher than what delta alone suggests.
When they diverge
The gap between delta-implied probability and true POP widens in several scenarios: credit spreads (POP is higher because of the premium buffer), skewed stocks with heavy put demand (delta overestimates downside probability), and high-IV environments where option pricing models assume larger tails. In practice, the difference is usually 2-5 percentage points, but for very wide spreads or in extreme IV, it can be 10%+.
Which one should you use?
Use delta for quick, rough strike selection — it is on every option chain and requires no calculation. Use POP when evaluating the full risk of a multi-leg trade, especially credit spreads and iron condors. VolRadar's Strategy Builder shows both: delta for individual legs and POP for the complete strategy, so you can compare them side by side.