Like Petrus, I only record business mileage. With my start and end mileage every year, it makes it easy to figure out the personal mileage if I ever need to.
I just keep track of it in Notes on my phone, backed up daily in the cloud. I tally the mileage at the end of the day, then once a month add it all together. Certainly not the most tech savvy way to go about it but it's free and accurate, and only adds one minute to the day, and another five minutes at the end of the month.