English muffins retain the best flavor and texture when they are frozen as soon as you get them home. If an English muffin is stale or otherwise over-the-hill, freezing it will not make it better. If you plan on eating your English muffins within a day or 2, there is no need to freeze them. How long your English muffins last in the freezer depends on the quality of your freezer and their location in the freezer. An English muffin in the door of your freezer, where is defrosts and refreezes repeatedly, is likely to get freezer burn quicker than an English muffin in the back of a freezer that keeps temperature well.  The coldest, most constant spot in your freezer is the center back.  Freezer burn is created when moisture from the food evaporates and then is refrozen. When a food is in the door of the freezer, it will develop freezer burn faster because it goes through freezing and thawing repeatedly. English muffins, like most breads, last a long time in the freezer. While they can last up to 6 months, it's a good idea to use them within a few months. After that, they can start to develop freezer burn and take on the taste of other foods in the freezer. Try to use your oldest frozen English muffins before those that you have just frozen. Using your oldest products first rotates your freezer's content and minimizes the chance of have freezer burned foods. English muffins that have been assembled into sandwiches can typically be stored for up to a month. This shortened freezer life is due to the moisture introduced by other ingredients and the amount of time the other ingredients can be frozen. Your English muffins might not be good any longer if ice develops on the inside of the plastic bag. This is a tell-tale sign that they have gotten freezer burn.  You should also look at the muffins themselves and see if they have any areas of discoloration. Areas that are very white are typically freezer-burned areas that will not taste good. Also look at the state of any toppings you put in preassembled English muffin sandwiches. If the toppings look discolored or dried out, then they are likely freezer burned.

Summary:
Freeze English muffins as soon as possible. Place the muffins in an area with a cold and constant temperature. Keep English muffins in the freezer for up to 6 months. Use pre-assembled sandwiches within 1 month. Look for signs of freezer burn and discoloration.