How often should I change my air filter?

Most manufacturers recommend changing the air filter every 12,000-20,000 miles or every 1-2 years. In dusty conditions or heavy urban traffic, change it more frequently (every 7,500-10,000 miles). A visual inspection is the best guide — if it looks dirty or grey, it is time to replace it.

Does a dirty air filter affect performance?

Yes, a dirty air filter restricts airflow to the engine, reducing power output and fuel efficiency. Studies show a clogged filter can reduce fuel economy by 2-10%. On older carburetted engines, the effect is more pronounced. Modern fuel-injected engines compensate somewhat but still suffer reduced efficiency.

Can I clean an air filter instead of replacing it?

Paper filters (the most common type) cannot be cleaned and must be replaced. Foam filters can sometimes be washed and re-oiled. High-performance cotton/gauze filters (like K&N) are designed to be cleaned and reused, typically lasting the life of the vehicle with regular cleaning every 50,000 miles.

What happens if I never change the air filter?

A severely clogged air filter can: reduce fuel economy by up to 10%, reduce engine power, increase engine wear (particles bypassing the filter), cause the engine to run rich (excess fuel), trigger check engine lights, and in extreme cases cause engine misfires or stalling.

Are expensive air filters worth it?

For most drivers, a standard OEM-quality paper filter (£8-£20) is perfectly adequate. Performance filters (£30-£60) may offer slightly better airflow but the difference on a standard car is minimal. Their main advantage is reusability, which saves money over many years.

CarCalcs

Air Filter Calculator — Replacement Interval

Calculate when your air filter needs replacing based on mileage and driving conditions.

Current Mileage

Last Filter Change (mileage)

Driving Conditions

Annual Mileage

Current MPG

Fuel Price

Filter Cost

How We Calculate This

Replacement Intervals

Clean conditions (motorway/rural): Every 20,000 miles
Normal conditions (mixed driving): Every 15,000 miles
Dusty conditions (construction, gravel): Every 10,000 miles
Severe conditions (unpaved, heavy pollution): Every 7,500 miles

Fuel Economy Impact

As the filter clogs, fuel efficiency drops. The calculator estimates MPG loss based on how far through the filter's life you are:

0-50% of life: negligible impact
50-75%: ~1% MPG loss
75-100%: ~3% MPG loss
Overdue: 5-10% MPG loss

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Actual figures may vary based on driving conditions, vehicle specifications, and other factors.