What probability of profit does and does not tell you
A probability of profit is a single number produced by a specific model. Understanding the model is the difference between using it and being misled by it.
How the number is produced
The calculator takes the range of prices at expiration where the position makes money, and integrates the assumed distribution of the stock price over that range. In this site's tools that distribution is lognormal, using the implied volatility of the chain.
That means POP is not a market fact. It is the output of an assumption: that the stock moves according to a lognormal distribution with volatility that stays where it is now.
Held to expiration: any profit taken or loss cut before expiry is outside the calculation.
No jumps: a gap through your strike is not a likely event in a lognormal world, and it is a common event in practice.
One volatility: skew and term structure are condensed into the numbers the model uses.
The number that sits next to it
A probability without a payoff is half a fact. What decides a strategy's outcome over many trades is the win rate required to break even, which is set by the ratio of what you risk to what you can make: required win rate = risk ÷ (risk + reward).
Risk $300 to make $100 and the position needs to win three times in four just to stand still. That is a 75% requirement, and it is visible without knowing anything about the stock — it comes entirely from the structure. A trade can therefore have a high probability of profit and still be a poor trade, if the loss on the losing occasions is far larger than the gain on the winning ones.
Why high-probability structures feel safer than they are
Credit structures — short puts, credit spreads, condors — naturally produce high POP numbers, because most of the time the stock does not travel far enough to reach the strike. The losses cluster in the minority of occasions, and they are larger.
The result is a P&L stream of many small wins punctuated by occasional large losses. That shape is easy to mistake for skill while it is working, and it gives no warning before the loss that pays for all of it.
Where POP stops being useful
POP ignores how much you make when right. It ignores the path, so it says nothing about a position that reaches a good profit in week one and expires worthless. It assumes you hold to the end, which is rarely what anyone does. And it is blind to position size, which is the variable that decides whether any of it matters.
Used as one input alongside the payoff curve, the probability of touching the strike, and the loss you would have to take, it is useful. Used as a verdict on its own, it is the most common way an options screen misleads a trader.
Questions
Is a 90% probability of profit a safe trade?
It says the position is profitable at expiration in the model nine times in ten. If the one losing occasion costs more than the nine wins combined, the strategy still loses money overall. Probability alone cannot answer that.
What win rate do I need to break even?
Risk divided by risk plus reward. Risking $3 to make $1 needs 75% of trades to win just to cover the losses; risking $1 to make $3 needs 25%. The structure sets the requirement before the market says anything.
Does POP account for volatility changes?
No. It treats implied volatility as fixed at the level used in the calculation, so an IV collapse or expansion after entry is outside the number — and for positions opened around events that is often the largest single factor.