Depends on your driving habits, quality of tune your car has, etc. Copper plugs are so cheap that I'd change them as frequently as feels right to you. Have an extra set sitting around, and whenever you're under the hood, pull your spark plugs, look at them. If they're good, throw them back in. If the electrode is rounded, pitch them.


Platinums are used OEM in probably 90% of the cars built today. No issues.