Unfortunately, film does not stay fresh forever. If you look at the box, you will see an expiration date. However, just because it is expired does not mean it can not be shot. There are just some things that need to be considered before shooting it.
How the film was stored before it expired has a big part to play in its outcome once shot. Film that was refrigerated will most likely come out looking better than film that was not. Film does not have to refrigerate before its expiration date but still should not be stored in conditions hotter than room temperature.
Shooting Expired Film
The general consensus is that expired film should be overexposed one stop for every decade that it is expired. The reason for this is that film loses its sensitivity to light more and more as it expires. However, sometimes it can still produce unpleasant results, so I overexpose one stop for every 5 years that the film is expired to help reduce grain and unpleasant color shifts. Sometimes when purchasing expired film, it does not have the packaging that shows the date of its expiration, so it is recommended that you bracket the film by overexposing one stop, two stops, and maybe even three stops if desired. I recommend staying away from film that is more than 10 years passed its expiration date. After 10 years is when the outcome of the film starts to become even more unpredictable.
Kodak Portra 400 expired in 2015 overexposed by 2 stops to retain shadow detail.
The type of expired film you shoot is another factor. Expired color positive/slide film does not handle expiration very well, so your best bet will be to shoot color negative, or B&W. Pro film will also perform better and has a better exposure latitude than consumer film which is necessary when overexposing film.
Example of expiration date on a box of Fuji Natura 1600.
Naturally, when shot correctly, expired film will have lower contrast due to fog or “fade” that is introduced. This can make for interesting and artistic looks. Especially when the film is no more than 10 years expired. It is also cheap and easy to find. Nowadays, it is hard to find color negative film in 35mm, so purchasing expired film can be a good alternative. Sometimes you can find a handful of rolls for the same price as one roll of Portra 800. Not to mention that you can find some unique film stocks that are no longer being made such as Fuji Natura and Superia 1600.
Unfortunately, expired film is cheap for a reason. Although it can produce interesting results, it can also come out completely blank or have extreme color shifts. The fact that expired film is unpredictable makes it not ideal for professional or important photos. The other caveat is that you lose versatility in terms of ISO rating because you would have to overexpose the film. This means that, in some cases, you can not use it in the same lighting conditions that it would otherwise perform well in.