assignment risk on writing american options

[gaussian]

Writing american options carry the following risks

1. They expire out of money
2. They are traded out of it before expiration
3. Some of them are exercised i.e. you get exercised.

My concerned is what if you get assigned to them before expiration. What are the chances of this happening before expiration for major indexes or large stocks ?

Everyone posting so far has missed the easiest point with options.

While you have a non-zero risk of getting assigned at any time when you are writing options the probability of this occurring is realistically near 0 in most cases. The cases it is not:

1. Violent moves in the underlying causing people to exercise the options you have written defensively at a massive loss (this is ok for you).

2. A dividend is approaching.

(2) is the most likely case of getting exercised early especially on large stocks. Don't hold short positions through ex-dividend. If the losses experienced exercising at a small loss are outpaced by the gains in dividend, it makes game theoretic sense to exercise.