Those costs and bills that give rise to legitimate tax deductions against income in Portugal – as opposed to those which do not – is a subject worthy of a fairly lengthy book. However, as a broad rule, those bills that are necessarily incurred in the operation of a business may typically be deducted.
So, the rental of offices, any employee related costs as well as the purchase and operation of office equipment (assuming that they are related to the operation of the business) may legitimately be deducted from any income before the payment of taxes.
More complex questions can sometimes arise where a telephone or vehicle are used partially for work and partially for personal use. Normally the percentage of the cost relating to work can be deducted but great care must be taken as in some cases the use of a vehicle may not be considered as a suitable deduction.