What counts as deductible business mileage versus non-deductible commuting?

The IRS never lets you deduct commuting, meaning the drive between home and a regular workplace, no matter how far. Deductible business mileage is travel between work locations: driving to a client, from one job site to another, to the bank for business, or to buy supplies. The big exception favors home-based businesses: if your home qualifies as your principal place of business, trips from there to clients and back count as deductible business miles, not commuting, which is a major reason the home office deduction pairs well with a car. Log the date, destination, purpose, and miles for each trip. Rounded 'guesstimates' at year-end are exactly what auditors disallow.