How often should I really change the oil?

For your vehicle, the manufacturer's Maintenance Minder (the oil life percentage) is designed to calculate the change interval based on how the engine is actually used, such as temperature, trip length and load. The 3,000-mile sticker is a generic reminder and is often more frequent than needed for modern synthetic oils.

Mostly highway driving is easy on oil, which is why your oil life is still at 40%. In general it is reasonable to follow the minder and change the oil when it asks, using the oil type and grade listed in your owner's manual. Many owners change it around 15% rather than waiting until 0%.

Two exceptions: change it sooner if you tow, drive in heavy dust, or do many very short trips, and still check the oil level between changes, because some engines use a little oil.