Every car is different. The best place to check is your owner's manual. Many manuals recommend anywhere from 3,500 to 10,000 miles. Some sites suggest every 3,000 miles. The
average miles driven per year is roughly 12,000 miles. The advantage of
changing it every 3,000 miles is that you can also have your car inspected on
average about 4 times a year. Many places that change your oil will also
do a routine check of other parts of your engine and car for free.
Changing your oil every 3,000 miles might be overkill, but you are also
getting such things as your belts, hoses, tires, radiator, inspection stickers,
etc. checked for free. An oil change costs about $20-25. $80-100 a
year for that peace of mind is worth it.