Thanks to constant reminders from dentists (and nagging parents), we know the golden rule when it comes to keeping our pearly whites in tip-top shape: Brush twice a day for two minutes and floss once. But all of that time spent brushing might be a waste if you’re using an old toothbrush.

“If the bristles are splayed or frayed, they won’t be pointing in the same direction, and they’re not as effective at cleaning your teeth,” explains Matt Messina, a dentist and spokesperson for the American Dental Association. Worn bristles mean that even a good brush could miss plaque and debris, says Alice Lee, a dentist and the associate director of pediatric dentistry at Montefiore Medical Center. So most dentists recommend replacing your toothbrush every three months or before wear and tear becomes noticeable. And yes, these guidelines also apply to replacing the heads of electric toothbrushes (sorry, wallet!).

Most dentists recommend replacing your toothbrush every three months.

Remembering to replace your toothbrush is easy, even if you don’t have superhuman memory. When you open a new brush, do some quick math, and write the date you need to bid it adieu at the bottom of your toothbrush in permanent marker.

One more thing: We don’t need to lose sleep over bacteria accumulating on the bristles of our toothbrush, which means there’s no need to chuck our brush every time we get sick, Messina says. “Bacteria in the mouth can’t survive a dry environment. So you don’t need to go to extreme measures to sterilize your brush.” Just make sure you rinse it after every use and store it with the bristles facing up in a convenient place where it can air-dry.