Can anyone here answer a tax question?

My husband is supposed to keep beginning and ending mileage on the car when he goes out of town for business. Every year I buy him a new planner for that purpose. As a salesman, that is a LOT of mileage. However, he’s very hit and miss about keeping track. He was so bad about it last year that when I went through the planner he had only noted about 5000 miles, when in years past it’s more like 15,000. This is important. It’s the difference between paying in to the feds or getting a refund.

My question is, rather than making note of each individual trip (although it’s not like it’s HARD to do!) can we take our beginning miles and ending mileage for the year and will they give us an assumptive personal mileage amount that we can deduct from that amount? It would make my life soooo much easier if that’s all we really had to do.

Since we have relatively complete records from the previous years (thanks to extreme diligence on my part) we have a record of average personal mileage used.

Will that work?