I am a small business owner that works out of my home office. My car trips are rarely as simple as driving from my home office to a business destination, then back to the home office. I am confused about how to safely calculate business mileage for a car trip that involves some business and some personal stops. As a theoretical example, image a single trip with the following segments:

1. Home office to Staples for some office supplies (2 miles)
2. Staples to grocery store for family groceries (4 miles)
3. Grocery Store to a customer's office to conduct business (8 miles)
4. Customer's office back to Home office. (6 miles)

Total mileage for trip = 20 miles

What is the maximum number of audit proof business miles I can claim for this trip and how to you calculate it?

1. Home office to Staples for some office supplies (2 miles)======> I do not think so; as you have an office in your home that qualifies as a principal place of business, you can deduct your daily transportation costs between your home and another work location in the same trade or business Or you can deduct the expenses of the daily round-trip transportation between your home and the temporary biz location. In general, commuting is considered personal use and is not deductible;however, as your home office is your principal place of work traveling to other sites where you do business may be deductible.
2. Staples to grocery store for family groceries (4 miles)===..Nondeductible as it is personal purpose trip NOT for business purposes .
3. Grocery Store to a customer's office to conduct business (8 miles)========>Nondeductible as said above.
4. Customer's office back to Home office. (6 miles)=======>Nondeductible. You can deduct the cost of round-trip transportation between your qualifying home office and your client’s or customer’s place of business.
Total mileage for trip = 20 miles

What is the maximum number of audit proof business miles I can claim for this trip and how to you calculate it?=======>>>>>>>There are two methods and you need to choose one of them;sinxe you use your car for business purposes, you may be able to deduct car expenses. You generally can use either actual expenses or the standard mileage rate. If you use the standard mileage rate for a year, you cannot deduct your actual car expenses for that year. If you want to use the standard mileage rate for a car you own, you must choose to use it in the first year the car is available for use in your business. Then in later years, you can choose to use either the standard mileage rate or actual expenses. If you do not choose to use the standard mileage rate, you may be able to deduct your actual car expenses such as
Depreciation Lease payments Registration fees
Licenses Repairs
Gas Oil Tires
Or etc; If you qualify touse both methods, before choosing a method, you may want to figure your deduction both ways to see which gives you a larger deduction.