Do you use your car for both business and private purposes? Then you need to determine what share of your mileage is professional. This percentage determines how much VAT you can reclaim on your car expenses and how much you can deduct on your personal income tax.
Please note that this article provides general guidance only. Tax rules may vary depending on your individual situation. When in doubt, ask your Tax Coach.
In this article, you will also learn which proof methods are accepted, when a mileage register is required, and how to enter your professional use percentage in Accountable.
💡 Why is it important to determine your professional use percentage?
The higher your professional use, the more you can deduct. The tax authorities will also expect you to be able to substantiate this percentage in case of an audit.
How much VAT you can reclaim on your car expenses
How much you can deduct on your personal income tax
👉 How do you calculate your professional use percentage?
The formula is simple: divide your business mileage by your total mileage.
(number of professional km per year ÷ total number of km per year) × 100
Example: in 2025, you drive a total of 20,000 km, of which 13,000 km are for professional purposes.
→ Your professional use: (13,000 ÷ 20,000) × 100 = 65%.
🚗 What about commuting to your usual workplace?
There is an important exception to keep in mind: your daily commute.
Your commute to a fixed workplace counts as private use, not professional use. Even though it is a trip you make for work, tax law treats it as private travel, for both VAT and personal income tax purposes.
📆 The 40-day rule: a location only counts as a "fixed workplace" (and therefore as commuting) if you are present there for 40 days or more during the year, not necessarily consecutively. If you work somewhere fewer than 40 days per year, for example at a client's site, in a co-working space, or on a temporary construction site, then that trip remains professional travel.
📄 What proof do you need to support your professional use percentage?
The VAT authorities allow you to choose between three methods for determining your professional use. Choose the method that best suits your situation.
Method | How does it work? |
1. Mileage register/log | You record every journey: the date, the departure and arrival addresses, the distance in kilometres, and the purpose of the journey. This is the most accurate, but also the most time-consuming, system. |
2. Home-work formula | A fixed formula based on your home-work distance: (home-work distance × 2 × 200 working days + 6,000 other private km) ÷ total km × 100 = % private use. Your home-work commute counts here as private, not as professional. Your professional use is 100% minus that private percentage. This only applies to 1 car per user, and you always use 200 days in the formula, even if you often work from home. |
3. Fixed 35% flat rate | The simplest option: you fix your professional use at 35%, without needing a mileage register. Note: you then need to stick to this for at least 4 consecutive calendar years, and apply it to all your mixed-use vehicles. |
✍ Is keeping a mileage register mandatory?
Not always; it depends on your professional use percentage.
Up to around 35%, a reasonable estimate is usually enough, for example based on your calendar or client visits.
From around 35% onwards, the tax authorities generally expect a mileage register or other detailed proof. The higher your percentage, the stronger the burden of proof needs to be.
✔️ How do you keep a mileage register?
You can keep a mileage log in a simple Excel or Google Sheets table. Make sure it meets the legal requirements.
In the log, enter:
date of the trip
starting and ending odometer readings
departure and arrival address
purpose of the trip (business or private)
Based on this data, you can total your kilometres and calculate your professional use percentage.
VAT deductibility vs. professional use: what's the difference?
Your professional use percentage is not the only percentage that matters for your car. There is also VAT deductibility, which is a separate, legally fixed rule specifically for vehicles.
35%: the legal flat rate. This is the default, and you don't need any proof to apply it.
50%: the legal maximum. You can only apply this if you can prove a higher business use, for example with a mileage register.
100%: only for professional drivers (taxi, delivery, rideshare, etc.), where the vehicle is used exclusively for the activity.
⚙️ How do you enter this in Accountable?
1. Professional use (per expense)
For each expense, you can indicate the professional percentage. For example, if you drive 35% professionally, enter this for every car expense. Accountable then automatically takes this into account for:
the VAT deduction;
and the calculation of your personal income tax.
2. VAT deductibility (once, in your car settings)
VAT deductibility works differently: you set it once per car, not per expense. When you add a passenger car under your car settings, indicate which VAT deductibility applies (35%, 50%, or 100%, see the section above). Accountable then applies this automatically to every expense linked to that car.
🚨 This VAT deductibility setting only applies to passenger cars. Utility vehicles follow different rules and are usually 100% deductible after professional use. You add the professional use directly to the expense, utility vehicles don't require you to add a car in the settings.
You simply need to encode the expense under the Utility vehicle category, then select the relevant subcategory. You don’t need to link a vehicle to the expense, since it is a utility vehicle and no CO₂ formula applies.
💡 Want to know more about how professional use works for your other expenses (phone, home office, laptop...)? Check out this article.
Key takeaways
Your professional use percentage determines how much VAT and income tax you can deduct on your car expenses.
Your daily commute to a fixed workplace counts as private use, not professional use.
You can choose between three methods: a mileage register, the home-work formula, or the fixed 35% flat rate.
From around 35% professional use, the tax authorities expect a mileage register or other detailed proof.
In Accountable, set your professional use percentage per expense, and your VAT deductibility once per car in your car settings.
Need help? Chat with us or email support@accountable.eu, we're happy to help.