35-40% is usually around 3-4,000 miles. I actually watch mine, and not the odometer. It calculates several factors and won't match the miles method but it IS consistent in it's opinion. In my opinion, whoever has everybody thinking today's oils can only go two or three thousand miles in a roller cammed engine ... must be working at a refinery. I change mine at 35-40% "oil life" though, because I drive almost every mile in heavy stop-and-go traffic.