Depends on many variables, but an overreaching broad answer would be most synth can go up to 10k miles, and I'd change the filter 1/2 way through the interval. Conventional oil, wouldn't push it past 5k miles. I use PP with OEM filter and change it every 5 - 7k miles. Probably overkill, but it gets me away for 30 minutes and gives me a reason to drink another beer.