You don't have to log your mileage every time you drive. Just record your mileage at the beginning of your fiscal year and again at the end of your fiscal year. And, as stated before, determine what percentage you used the vehicle for business and that will be your deduction. I keep all receipts for fuel and maintenance and total that at the end of the year. I then figure my mileage deduction and whatever is greater, that is what is deducted.