The following people do not need a visa to enter Portugal:
Citizens of the Schengen area: Austria, Belgium, Bulgaria, Croatia, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden and Switzerland;
Nationals of Albania*, Andorra, Antigua and Barbuda, Argentina, Australia, the Bahamas, Barbados, Bosnia and Herzegovina*, Brazil, Brunei Darussalam, Canada, Chile, Colombia, Costa Rica, Dominica, El Salvador, Georgia, Grenada, Guatemala, the Holy See (Vatican City State), Honduras, Israel, Japan, Kiribati, North Macedonia*, Malaysia, Marshall Islands, Mauritius, Mexico, Micronesia, Moldova*, Monaco, Montenegro*, New Zealand, Nicaragua, Palau, Panama, Paraguay, Peru, Samoa, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, San Marino, Serbia**, the Seychelles, Singapore, Solomon Islands, South Korea, Taiwan***, Timor-Leste, Tonga, Ukraine*, the United Arab emirates, the United States of America, Uruguay, Vanuatu and Venezuela;
Bearers of passports issued by the Hong Kong special administrative region (People’s Republic of China) and the Macao special administrative region (People’s Republic of China);
Nationals of the United Kingdom can travel to countries in the Schengen area for up to 90 days in any 180-day period without a visa. This applies if they travel as a tourist, to visit family or friends, to attend business meetings, cultural or sports events, or for short-term studies or training. At Portuguese border control, they may need to use separate lanes from EU, EEA and Swiss citizens when queueing.
* Bearers of biometric passports only
** Bearers of biometric passports only, excluding holders of Serbian passports issued by the Serbian Coordination Directorate (in Serbian: Koordinaciona uprava)
*** Bearers of biometric passports bearing identity card number.
The following people need a visa to enter Portugal (along with a valid travel document):
Nationals of Afghanistan, Armenia, Angola, Azerbaijan, Bangladesh, Burkina Faso, Bahrain, Burundi, Benin, Bolivia, Bhutan, Botswana, Belarus, Belize, Democratic Republic of the Congo, Central African Republic, Congo, Côte d'Ivoire, Cameroon, China, Cuba, Cape Verde, Djibouti, Dominican Republic, Algeria, Ecuador, Egypt, Eritrea, Eswatini, Ethiopia, Fiji, Gabon, Ghana ,The Gambia, Guinea, Equatorial Guinea, Guinea-Bissau, Guyana, Haiti, Indonesia, India, Iraq, Iran, Jamaica, Jordan, Kenya, Kyrgyzstan, Cambodia, Comoros, North Korea, Kuwait, Kazakhstan, Laos, Lebanon, Sri Lanka, Liberia, Lesotho, Libya, Morocco, Madagascar, Mali, Myanmar/Burma, Mongolia, Mauritania, Maldives, Malawi, Mozambique, Namibia, Niger, Nigeria, Nepal, Oman, Papua New Guinea, Philippines, Pakistan, Qatar, Russia, Rwanda, Saudi Arabia, Sudan, Sierra Leone, Senegal, Somalia, Suriname, South Sudan, São Tomé and Príncipe, Syria, Chad, Togo, Thailand, Tajikistan, Turkmenistan, Tunisia, Turkey, Tanzania, Uganda, Uzbekistan, Vietnam, Yemen, South Africa, Zambia and Zimbabwe;
Nationals of the entities and territorial authorities that are not recognised as states by at least one Member State: Kosovo as defined by the United Nations Security Council Resolution 1244 of 10 June 1999, and the Palestinian Authority.
Schengen visas may be single-, double- or multiple-entry and allow the holder to spend no more than 90 days in Portugal and other Schengen countries within a 180-day period (calculated from the holder’s first arrival in the Schengen area).
If you require a visa to enter Portugal and are planning to stay for more than 90 days, then you must apply for a Portuguese visa, not a Schengen visa.
The European Commission has a short-stay Schengen visa calculator at https://ec.europa.eu/home-affairs/content/visa-calculator_en, which you can use to calculate whether you fulfil the general 90 days/180-day rule or not, and to estimate for the maximum length of stays in the future from the intended date of entry on the basis of previous entry and exit dates.