How often should you do it?

Straight answers to the recurring-interval questions people actually search for — oil, filters, sheets, feeds. Each page gives the interval, what changes it, and how to tell.

Then the part an answer cannot cover: knowing when you last did it. That is what When Last is for.

Car maintenance

• How often should I change my oil?On full synthetic oil in a modern engine: every 7,500–10,000 miles (12,000–16,000 km) or once a year, whichever comes first.
• How often should I change my cabin air filter?Every 15,000–30,000 miles (24,000–48,000 km), or about once a year.
• How often should I change my engine air filter?Every 15,000–30,000 miles (24,000–48,000 km) for ordinary driving, and every 10,000–15,000 miles if you spend time on dusty or unpaved roads.
• How often should I change my spark plugs?Iridium 60,000–100,000 miles, platinum around 60,000, copper 20,000–30,000 — the plug material decides it.
• How often should I change my transmission fluid?Conventional automatic: every 60,000–100,000 miles (100,000–160,000 km) in normal use, and every 30,000–60,000 miles if you tow or sit in traffic.
• How often should I rotate my tires?Every 5,000–8,000 miles (8,000–13,000 km) — for most people, that lands neatly on every oil change.

Around the house

• How often should I change my bed sheets?Once a week for most people.
• How often should I change my toothbrush?Every 3–4 months, or sooner the moment the bristles start to splay outward.
• How often should I change my furnace filter?A 1-inch pleated filter every 1–3 months, a 4-inch media filter every 6–12 — thickness decides it.
• How often should I backwash my pool?Not on a calendar: when the filter pressure gauge reads 8–10 psi above its clean starting pressure, which in season usually works out to every 1–2 weeks.

Pets, plants and kitchen

• How often should I feed my cat?Adult cats: twice a day as a minimum, and up to 4–5 small meals if that suits your schedule — cats are natural frequent grazers.
• How often should I feed my dog?Adult dogs: twice a day, roughly 8–12 hours apart.
• How often should I feed my betta fish?Once or twice a day, 3–4 pellets per meal — as much as the fish clears in about two minutes and no more.
• How often should I feed my sourdough starter?At room temperature: every 12 hours at a 1:1:1 ratio.
• How often should I fertilize my tomato plants?In garden soil: every 2–3 weeks once the first fruit has set.