How often should a homeowner replace their air conditioner's air filter?

When your air filters seem dirty from a visual point, you need to change them. However, there a number factors that an owner can be used as a standard, depending on: 1.  Type of filter your A/C system requires, the overall air quality of your city where your home is located.

2.  Pets – Birds, cats, dogs, hamsters (do you have one?), etc.

3.  Number of occupants in the house
In summary; Home that is not occupied by regular base or single occupant homes without pets or allergies may get away with changing the filters every 6-12 months, but typical suburban home with that is used 90% daily and pets will probably need to change every 90 days.

Source: 
https://desk.zoho.com/portal/cetmgtsol/kb/articles/how-often-should-a-homeowner-replace-their-air-conditioner-s-air-filter