Mobile phone & internet costs

That is up to you, of course. If you only use your mobile phone for your professional activities (e.g. if you have two, one for private use and one for work), you can deduct 100%. In other cases, you will have to make an estimate based on your invoices (question a detailed list of all phone numbers, texts and other services so that you can see for yourself what percentage you use for professional and private purposes from the times and dates). For fixed costs (not linked to usage), you then calculate the same percentage. This raises a question, but in my case (I use one phone number from my employer during the week solely for my work as an employee, and I have one phone number that I use both privately and for my self-employed in secondary occupation), it is worth the effort because I arrive at 85% professional use for telephony. I apply the same percentage for the internet (because I mainly do a lot of digital work).

Johan