I always forget to replace my toothbrush at the recommended time interval and would go much longer that I was supposed to. To remind me to replace my toothbrush I setup a repeating task that reminds me to replace my toothbrush every three months.

I do the same thing for my water filters, air filters, and sponges in the house. The great thing is that each item can have it's own time interval in a single list.

I recommend that you use a "repeat after" task so you only get a new task once you've completed it. For example:

Replace toothbrush after 3 months