(a) Periodical income declaration: must be submitted until the last working day of May if the fiscal year corresponds to the civil year or five months after the term of the fiscal year if different from the civil year;

(b) Annual Simplified Company Information (IES): must be submitted until the last working day of June if the fiscal year corresponds to the civil year or six months after the term of the fiscal year if different from the civil year;

(c) Periodical VAT declaration: for a turnover of or above €650.000,00 in the precedent civil year, until the 10th day of the second month following the one to which the operations refer to. Otherwise, until the 15th day of the second month following the quarter to which the operations refer to.
The companies must submit declarations of registrations, changes or cancellations whenever such situations occur, as well as periodic statistical information requested by the Regional Secretary of Statistics, the National Institute of Statistics and the Bank of Portugal

Personal Income Tax (IRS) and Social Security Taxes

Companies are required to withhold personal income tax and social security contributions on the payment of salaries and other forms of remuneration to their workers. The applicable rates are as follows:

(a) IRS: rates vary according to the level of the salary paid;

(b) Social Security: a fixed rate of 11% for the employee and of 23,75% for the employer, for Directors the rate of 23,75% paid by the company and 11% paid by the Director.

The both amounts (IRS and Social Security) must be paid until the 20th day of the following month in which the deductions were made.

– See more at: http://tpmc.pt/index.php/en/useful-informations/corporate-tax-returns#sthash.k0BWTWdW.dpuf