The Portuguese postal code (código postal) is formed by four digits, a hyphen, then three digits, followed by a postal location of up to 25 characters in capitals.
Avenida Marconi 4C 1000-205 Lisboa[1]
Postal codes are given at the building block level and also to designated addresses with high volumes of mail. The first digit designates one of nine postal regions; the following two digits designate postal distribution centers; the fourth digit is 0 if it belongs to a capital of municipality, 5 if not, or any other digit if it is a designated address; the last three digits sort building blocks and designated addresses. The more important the city, the more rounded is the number formed by the first four digits.
Prior to 1976, only Lisbon had used a system, of six zones (Lisboa 1 to Lisboa 6).
Avenida Padre Manuel da Nobrega 14, 2º Esq. Lisboa 1[2]
In 1976, a national postal code system was introduced, with a four-digit structure, and designated addresses added "CODEX" (abbreviation of código extraordinário) to the postal location:
Instituto de Hidráulicas e Recursos Hídricos Rua dos Bragas 4099 Porto CODEX[3]