Every furnace filter is different. There are two things you must consider when answering this question: What household influences affect my filter? and What type of filter do I currently have? There are four types of filters:
Disposable- Sold in the $1.50-$4.00 range. These filters need to be changed monthly.
Pleated- Sold in the $6.00-$20.00 range. Manufacturers recommend 1-3 months.
Washable- Sold in the $10.00-$20.00 range. Need to be washed monthly.
Media Filter- Sold in the $25.00-$70.00 range. Need to be changed bi-yearly to yearly.
Household influences have a big affect on how often your furnace filter should be changed. Pets, children, home renovations, and the age of your home all contribute to the amount of dust and particles expected to be caught by the furnace filter. What may work for your neighbor may not work for you. Set reminders on your computer or phone to help remind you to check your filter.