You need to have the total miles as well as the business miles in order to claim your vehicle expense. Try finding service records for your vehicle near the beginning and the end of the year. Those usually will list the odometer readings so that you can get a good idea of the total miles driven for the year. If you consistently have your oil changed or tires rotated at a particular place, they may be able to help you with the records.
Thank you for your response. Do I have to claim the miles? Or can I not use them at all for a deduction?
If you are using the standard mileage rate, as opposed to the actual costs method, you can just estimate the total miles you drove for the year. But if you are using the actual method where you deducting gas, repairs & maintenance, insurance, etc. and taking depreciation then it is important to know your actual mileage for the year.