Changing your ac air filter is important to keep your HVAC system running smoothly and efficiently.
As a rule of thumb, the easiest way to remember to replace your air filters is when the seasons change. It is June now, schools are out, and summer heat is starting to rise, causing your air conditioner system to work harder and longer. Whereas in the spring, you have more pollen in the air, and your filters are vital to filtering the pollen from your house.
Typically filter manufactures suggest every 90 days for air filter replacement, and I try to schedule my replacements with the beginning of winter, spring, summer, and fall.
If you have allergies, or if you have pets in your house, you may want to consider changing out your filters more frequently, about every other month.
Other factors are important to consider too, like whether you live in a large city where air quality and pollution are a concern. Or if you live out in the country, with good air quality, you could possibly get by with replacing your filters less frequently.
Most importantly, although everybody forgets to change their furnace and ac filters once in a while, so at the very least change them when you can, and try to set up a schedule and get reminders.