My wife kept track of her mileage for work but not the total number of miles on the vehicle for 2018. Does the total have to be accurate if I know the total for work?

If these miles are for her job that works for an employer, that is no longer deductible because of tax reform. The act passed last year suspended the deduction for unreimbursed employee expenses.

If they are for self-employment, they can be deducted and you should use your best estimate for personal mileage.