(2025) When can I deduct communication costs?

You can deduct your telephone and internet costs from tax if they were work-related. Deductible communication costs as business expenses include the work-related portion of the basic fee for your telephone line and the call charges or flat rate for a landline or mobile phone, as well as the fees for sending work-related faxes and the costs of work-related internet use.

If you have a second telephone line in your home office that you use exclusively for work (at least 90% work-related use), you can claim these costs in full. However, this does not apply to the use of a work-related secondary number on the same ISDN telephone line.

In this case, you must declare your work-related cost share separately. If you cannot settle your work-related costs on a flat-rate basis, it is also possible to provide individual proof of calls, faxes, and internet use. A record of the work-related share for a period of three consecutive months is sufficient for this purpose.