There is much debate over how long your filters will last for. I have heard physicians says anywhere from 40 hours, 30 days to 2 years.
My answer is that these will last you probably 1-2 years or the duration of the pandemic if treated properly. But let’s see what 3M says.
First we should clarify that we are only talking about particulate filters. There are numerous types of 3M filters but we are only interested in the particulate filters. N95, P95, P100… It doesn’t matter. These are usually color designated by their magenta color or what most of us call pink.
The myth of 40 hours or 30 days originates from the combination filters. Some combination filters have both a gas/vapor filter and a separate particulate filter. The limitations on these filters refer to the gas/vapor portion, not the particulate filter. Since you aren’t being sprayed with mustard gas or using vaporized hydrogen peroxide you can ignore that.
Just be aware that 3M has been slowly changing several of their online safety PDFs. This one used to be more specific saying that particulate filters could be used until there is resistance to breathing. Now it doesn’t say anything specific to particulate filters.
This 3M video also says when they are dirty, damaged or difficult to breathe through.
This 3M Australia/New Zealand filter guide says that they actually become a more effective filter the more they become clogged and essentially that they can be used until breathing is difficult:
Here is some more comprehensive information on respirators below: