Options assignment probability calculator: what delta roughly says
The option chain already carries a rough answer to “how likely is assignment?” — it's the delta. Type it in and see what it roughly means, and why it is a model number and not a fact.
How it works: delta is a number on the option chain between 0 and 1 (puts show it as negative). Traders use its size as a rough chance that the option ends up in the money at expiry — which, for an option you sold, is the chance of assignment. The chance the stock touches the strike at some point before expiry is roughly twice that, because touching once is easier than still being past it on the last day. These are model numbers read off the option's own price. They are not a forecast or a promise, and they say nothing about how far past the strike the stock could go.
Why "30% chance" is not a fact
Delta comes from a pricing model fed with the market's current guess at how much the stock moves. Change the guess and delta changes. A news event, an earnings date inside the trade, or a market-wide drop can turn a 0.30 put into a 0.70 put in a day. So read the number as "the market is pricing this as about 3 in 10 today", not as odds you can bank. The market's guess at volatility is explained in how to read an options chain.
What the number is good for
Comparing strikes on the same stock. A 0.15 put and a 0.35 put on the same expiry are different promises, and delta tells you which is which. In the wheel strategy that is the whole use of it: pick a strike where assignment is a price you'd be glad to pay, not a strike where the premium looks biggest. Delta also doesn't tell you the loss if assigned — that depends on how far the stock fell, which is why the cash-secured put calculator shows the result at a range of prices.
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