A slightly lower IRS mileage rate means smaller tax deductions for business miles in 2020. The optional standard mileage rate used to calculate the deductible costs of operating an auto for business has decreased by by one-half cent to 57.5 cents per mile. It was 58 cents for 2019 and 54.5 cents for 2018. This mileage rate comes into play if you don’t want to keep track of actual vehicle-related expenses. But you still must record certain information, such as the mileage, date and destination for each trip. The mileage rate can also be used for reimbursing employees. Many rules and limits apply.