You deduct gas costs

audit red flags driving gas

Most employers reimburse you for driving-related costs like gas. So if you try to deduct hundreds or thousands of dollars' worth of automobile costs as a business expense, that's going to raise eyebrows at the IRS.

"If you happen to work for an employer who doesn't have a policy for reimbursing you for auto expenses, the IRS would want to understand your employer's policy, since generally companies will reimburse you for any expenses related to the business," said Connolly.

And if you own a business, you can only deduct business-related costs. The gas you buy for your personal driving costs cannot be mixed up in that, or the IRS will ask for documentation of everything.

First published March 9, 2015: 10:35 AM ET

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