# what is exercise frontier in option pricing

What's exercise frontier in option pricing? It kept popping up but I was never fully introduced to the concept.

Follow up question: And is the optimal exercise time the first time the option is in-the-money or is it the time where (value_exercise_now - value_continue) is at its largest?

Someone please shed some light thanks!

The early exercise boundary (or frontier) for American puts is the level $S^*(t)$ where it is optimal to exercise the put if $S(t)<S^*(t)$. There is no known analytical formula for it, but it can be approximated in various ways.