How often should you replace it?

Some chores run on a calendar you never see. Nobody remembers the day they opened a new toothbrush or put in a furnace filter. So when the question comes up, the honest answer is usually “a while ago”. Here is what official sources recommend for the most common ones, and where their advice has caveats.

The short version

Toothbrush: every 3 to 4 months

The American Dental Association recommends a new toothbrush, or a new head for an electric one, every three to four months. Replace it sooner if the bristles look matted or frayed, because a worn brush cleans less well. Children’s brushes often wear out faster.

Sheets and pillowcases: once a week

The Sleep Foundation’s advice for most people is to wash sheets and pillowcases weekly. If you don’t sleep in the bed every night, every two weeks can be enough. If a pet sleeps in the bed, they suggest every three to four days. Sweating a lot, allergies and illness are also reasons to wash more often.

For the rest of the bed, the same guidance puts duvet covers at every two weeks to a month, comforters and blankets at every two to three months, and washable pillows at every four to six months.

Contact lens case: at least every 3 months

The CDC says to replace your lens case at least every three months, because germs can grow in a case even when you clean it properly. Between replacements, rub and rinse the case with solution, leave it upside down with the caps off to dry, and use only fresh solution. Don’t top up old solution. The FDA gives the same three-month interval “or as directed by your eye care professional”.

Furnace and AC filter: check monthly

ENERGY STAR says to check the filter every month, especially in winter and summer when the system runs most. Change it if it looks dirty after a month, and at the latest every three months. A clogged filter makes the system work harder, which costs energy and can shorten its life. Some systems use a reusable filter that you clean instead.

Smoke alarms: test monthly, replace at 10 years

The U.S. Fire Administration and the NFPA both say to press the test button on every smoke alarm at least once a month. The whole alarm needs replacing 10 years after the manufacture date printed on the back, not the date you bought it. Replace it sooner if it doesn’t sound during a test.

Alarms that take a 9-volt battery need a new battery at least once a year, and hard-wired alarms usually have a backup battery on the same schedule. Sealed 10-year alarms don’t need battery changes.

Fridge: spills now, leftovers weekly

U.S. food safety agencies don’t set a deep-cleaning schedule for the fridge. They do say to wipe up spills right away, which helps stop Listeria growing and juices from raw meat reaching other food. USDA suggests clearing out perishables once a week. As a rule of thumb, cooked leftovers keep about four days, and raw poultry and ground meat one to two days.

Dental check-up: your dentist sets it

Six months is a habit, not a rule. In the UK, NICE guidance says the gap between check-ups should be anywhere from 3 months to 2 years, or up to 1 year for under-18s. Your dentist picks the interval from the state of your mouth and reviews it at each visit. People with good oral health may only need to go every 12 to 24 months. Don’t wait for the date if you have pain or bleeding gums.

Eye exam: depends on age

For adults with no risk factors, the American Academy of Ophthalmology suggests a comprehensive eye exam every 5 to 10 years under 40, every 2 to 4 years from 40 to 54, every 1 to 3 years from 55 to 64, and every 1 to 2 years from 65. The American Optometric Association recommends more frequent exams for younger adults. Both agree that diabetes, a family history of eye disease and other risk factors call for a personal schedule, so ask your eye doctor.

The hard part is remembering when

Knowing the interval is the easy half. “Every three months” only works if you know when the last time was, and most of us don’t. A recurring calendar event helps for fixed dates like the smoke alarm test. It doesn’t fit things you do when you get to them, like the filter you changed two weeks late, which moves every date after it.

What works better is writing down the date each time you do it and counting from there. That is what Oncelet is for. You tap once when you change the filter or open a new toothbrush, and it shows how many days it has been. After four entries it knows your usual interval, and you can set a reminder so the next one doesn’t slip.

Sources

1. American Dental Association. Toothbrushes, ADA Library.
2. Sleep Foundation. How Often Should You Wash Your Sheets?
3. Centers for Disease Control and Prevention. Preventing Eye Infections When Wearing Contacts.
4. U.S. Food and Drug Administration. Contact Lens Solutions and Products.
5. ENERGY STAR. Heat & Cool Efficiently.
6. U.S. Fire Administration. Smoke Alarms.
7. National Fire Protection Association. Smoke Alarms safety tip sheet (PDF).
8. USDA Food Safety and Inspection Service. Refrigeration and Food Safety.
9. U.S. Food and Drug Administration. Are You Storing Food Safely?
10. NICE. Dental checks: how often should I come back for a check-up? (CG19).
11. NHS. Dental check-ups.
12. American Academy of Ophthalmology. Eye Exam and Vision Testing Basics and Frequency of Ocular Examinations.
13. American Optometric Association. New AOA adult eye guideline.