I'm not sure if someone mentioned this above, but I can't think of any good reason to exercise a put option. Sometimes people exercise a call option in order to capture a dividend, but when you exercise a put option, you're throwing away all time premium (extrinsic value) left in the put option. Since american options can be exercised at any time, the premium of the put option will contain both intrinsic (if the option is ITM) and extrinsic (time premium). The intrinsic value will always be equal to the amount that the option is ITM because someone holding the option can exercise it at any time and always get that amount. Only case that I can think of to exercise is if the option is way deep in the money or not liquid so that the bid / ask spread is wide, but even then if the option is priced just one cent or two less than the intrinsic value, someone will buy as they could use it as part of a risk free trade. Also, most brokers aside from IB charge an extra fee for exercise / assignment.