Tax Basics & Filing Requirements

Startup with One Car: Business and Personal Use Tax Rules

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Written byLipai WangFounder · IRS-registered tax professional

Key Takeaways

Business use: client visits, product delivery, between business locations
Personal use: commuting, errands, groceries, vacation — never deductible
Two methods: Standard Mileage Rate or Actual Expense Method
A contemporaneous mileage log is required — no log means no deduction
Commuting from home to regular workplace is always personal

Mixed-Use Vehicle: Business vs. Personal

When a startup has only one car used for both business and personal purposes, properly distinguishing between business and personal use is critical. Driving to meet clients, delivering products, traveling between business locations, and visiting suppliers are all business use. Driving to the grocery store, picking up children, and vacation trips are 100% personal and never deductible.

Two Methods for Deducting Vehicle Expenses

The IRS allows two methods. The Standard Mileage Rate method multiplies your business miles by the IRS-set rate (adjusted annually). The Actual Expense Method tracks all vehicle costs (gas, insurance, repairs, depreciation) and deducts the business-use percentage.

Both methods require a contemporaneous mileage log documenting the date, destination, business purpose, and miles driven for each business trip. Without a log, the IRS can disallow the entire deduction.

Common Mistakes to Avoid

The biggest mistake is claiming commuting miles as business use. Driving from home to your regular workplace is commuting — always personal, never deductible. However, driving from your home office (if you have a qualified home office) to a client meeting IS business use.

Another common error is inflating business mileage percentages. The IRS can compare your claimed business mileage against total mileage on the odometer. Significant discrepancies will trigger scrutiny.

Frequently Asked Questions

Can I switch between mileage methods each year?

If you use the Standard Mileage Rate in the first year, you can switch to Actual Expenses in later years (with some restrictions on depreciation methods). If you start with Actual Expenses, you can generally switch to Standard Mileage Rate in later years.

What if I use the car 90% for business?

If your business use is more than 50%, you can use either method. The higher the business percentage, the larger your deduction. But be prepared to substantiate the percentage with a mileage log.

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