Why these deductions need extra care
Business mileage and home office costs are two of the most useful deductions for freelancers and small business owners, and two of the easiest to get wrong. Both involve things you also use privately: your car and your home. That makes them a natural place for a tax authority to ask questions, and the answer they expect is not a rough estimate but a record made at the time. A receipt for a software subscription speaks for itself. A claim for 6,000 business kilometres or 15 percent of your rent needs a log or calculation behind it. The good news is that the records are simple to keep once you have a habit. The rules on what you can claim differ by country, so check the details with your tax office or accountant.
What a mileage log should contain
A mileage log is a record of each business trip, written at or near the time you made it. For every trip, note the date, where you started and where you went, the purpose of the trip, such as a client meeting or picking up supplies, and the distance driven. Many people also record the odometer reading at the start and end of each trip, and in some countries that is expected. At the start and end of the year, note the total odometer reading so you can show business kilometres as a share of all driving. A log filled in from memory at year end is weak evidence and may not be accepted. A simple notebook in the car, a spreadsheet or a phone note works fine, as long as you fill it in every time.
Business trips versus commuting
Not every drive you make for work counts as business mileage. In many tax systems, the regular trip between your home and your normal place of work is treated as commuting, which is a private cost, even if you are self-employed. Trips from your base to a client's office, to a supplier, to a temporary work site or between two business locations are more likely to count. If your home is your main place of business, trips from home to clients are often treated as business travel, but this depends on local rules. Personal stops on a business trip, such as a detour to the shops, should be left out of the distance. Because the definitions vary, find out exactly how your country draws the line before you start logging.
Fixed rate or actual costs
Many countries let you claim vehicle costs in one of two ways. The first is a fixed rate per kilometre or mile, set by the tax authority, which you multiply by your business distance. It is simple, needs only the mileage log, and the rate is meant to cover fuel, wear, insurance and depreciation. The second is to claim the actual costs of running the vehicle, such as fuel, servicing, insurance, tax and depreciation, multiplied by the business share of total driving. This needs every receipt for the year in addition to the log, but can be worth more for a vehicle used mainly for business. Some countries allow only one method, or restrict switching between them. Look up the current official rate rather than relying on an old figure, as rates change.
A sample log entry
Here is what a few lines of a good log look like in practice. On 3 March, from home office to Brightline Studio in the city centre and back, for a project kick-off meeting, 34 km. On 7 March, from home office to the print shop to collect client brochures, then to the client's office for delivery, and back, 52 km. On 12 March, from home office to the train station for a client workshop in another city, 18 km, with the train ticket recorded separately as a travel expense. Each entry answers four questions: when, where, why and how far. If you track odometer readings, add them to each line. At the end of the month, total the business distance. Twelve monthly totals added together give you the figure for your return.
Working out your home office share
For the home office, the key number is the share of your home used for business. A common method is floor area. Measure the room or space you use for work and divide it by the total floor area of your home. If your office is 12 square metres in an 80 square metre flat, your business share is 15 percent. Some systems instead use the number of rooms, or let you choose a fixed flat-rate amount based on hours worked from home, which requires no calculation of costs at all. Most systems expect the space to be used regularly, and often exclusively, for work; a dining table where you also eat usually does not qualify. Write down how you measured and why the space qualifies, and take a photo of the setup.
Which home bills to keep
If you claim actual costs rather than a flat rate, you apply your business share to the household bills that relate to the space. Depending on your country, that may include rent or mortgage interest, electricity, heating, water, building insurance, property service charges and cleaning. Using the example above, if your annual rent is €14,400 and your share is 15 percent, the business part is €2,160. Keep every bill you include, for the full year, along with a short note of your calculation. Repairs that relate only to the office, such as painting that room, may be claimable in full in some systems, while repairs to the whole home are usually split by the same share. Keep these records as long as your other tax records; our guide on how long to keep receipts explains the typical periods.
Phone, internet and other mixed costs
The same logic applies to other costs you use for both work and private life. For a phone or internet connection, work out a reasonable business share and keep a note of how you arrived at it, for example by looking at a typical month of calls or usage. If you have a separate business phone line, it can usually be claimed in full. For equipment such as a laptop that you also use privately, many systems expect you to claim only the business share. Be consistent from year to year, and be prepared to explain your percentage if asked. A sensible, documented figure is far safer than claiming 100 percent of something you clearly also use at weekends. For more on what usually counts as deductible, see our small business tax tips.
Keep the receipts with the expense
A good log is only half the record; the receipts behind it matter just as much. In Kelvo Books, you can log fuel, parking, train tickets and household bills as expenses, photograph the receipt so the amount and date are read for you, and attach it to the expense in one step. On Pro, forward digital bills and booking confirmations to your personal @kelvo.app address and they are recorded automatically. Each expense flows into your live profit and loss and quarterly tax summary, and a CSV export gives your accountant everything at year end. The free plan includes 10 invoices a month, unlimited clients and expenses, and the P&L. Pro is €7 a month. Start at books.kelvo.app.