Both of my vehicles tell me when my oil shelf live is nearing it's end. One of my vehicles uses sythetic oil, the other conventional. The old 4X4 uses regular oil and I get it changed every 5,000K. The little sporty deal uses synthetic oil which can last up to 15,000K, but I'll follow what my onboard computor tells me. For example if  a yellow light comes on and says "Oil life is 15%" then it's time to book an appointment at the garage.