If you are self employed or if you have a job where you drive a lot and don't get reimbursed for mileage by your employer, make sure you keep a log of your automobile mileage each year.
You need to calculate your business miles as a percentage of total miles annually, then use either the business miles at 54.5 cents a mile in 2018 (a bonus: 58 cents a mile in 2019) or use the percentage to calculate your actual auto expense. If you get audited, your auto log (complete with beginning and ending odometer readings and the purpose of all the business travel daily) is the only piece of taxpayer prepared information that the IRS auditor is supposed to accept (but it doesn't hurt to give the auditor a couple of auto repair bills that tie to the odometer readings that are in the log).
I have been involved in many IRS audits where the automobile expenses were looked at by the auditor and I am pleased to say that to date I have never had a change to taxpayer auto expenses because of the mileage percentages (once we had a problem with some of the actual auto expense documentation, but if the taxpayer took the standard mileage deduction, none of the deductions were changed.)
There are now apps available that allow your phone to track your mileage; some work really good, but make sure if you use one that it keeps track of your odometer readings (it may direct you to input the amount at the first of the year and will update through all mileage, which means you will have to put in all mileage driven, not just business mileage) and make sure you can print up the log at least as a PDF so you can send to your computer to print up.
For more information, call or email me and we can discuss it.