Chance of profit

Also called Probability of profit, POP

The chance a position finishes in profit at the chosen date, from the legs' implied volatility.

Chance of profit is the share of possible prices at the chosen date where the position makes money, weighted by how likely each price is. Theta Vantage takes the price at that date as lognormal, with the volatility of the position's legs (each leg's implied volatility, weighted by its size, times the calculator's IV slider) and the rate, and adds up the probability over every stretch of prices where profit and loss is above zero.

Reading it

It's a model's number. It assumes the options are priced right and moves follow the lognormal curve, which understates large moves. It also says nothing about size: a 90% chance of a small profit with a 10% chance of a large loss can be a poor trade. Read it with the max loss and return on risk.

In Theta Vantage

The strategy calculator's summary shows it for the selected date. Move the date slider and it changes with the position.