Share your insights or perspective on the financial matter presented in the input.

Why can it be a bad idea to buy stocks after hours?
There are several reasons it is not recommended to trade stocks pre- or post-market, meaning outside of RTH (regular trading hours). Since your question is not very detailed I have to assume you trade with a time horizon of at least more than a day, meaning you do not trade intra-day. If this is true, all of the above points are a non-issue for you and a different set of points becomes important. As a general rule, using (3) is the safest regardless of what and how you trade because you get price guarantee in trade for execution guarantee. In the case of mid to longer term trading (1 week+) any of those points is viable, depending on how you want to do things, what your style is and what is the most comfortable for you. A few remarks though: (2) are market orders, so if the open is quite the ride and you are in the back of the execution queue, you can get significant slippage. (1) may require (live) data of the post-market session, which is often not easy to come by for the entire US stock universe. Depending on your physical execution method (phone, fax, online), you may lack accurate information of the post-market. If you want to execute orders based on RTH and only want to do that after hours because of personal schedule constraints, this is not really important. Personally I would always recommend (3), independent of the use case because it allows you more control over your orders and their fills. TL;DR: If you are trading long-term it does not really matter. If you go down to the intra-day level of holding time, it becomes relevant.