Holidays in Sao Tome and Principe

Official national public holidays. Regional and religious observances may vary by area.

About Time in Sao Tome and Principe

São Tomé Spent One Calendar Year an Hour Ahead of UTC

At the end of 2017, São Tomé and Príncipe did something rare for a country close to the Greenwich meridian: it deliberately moved its legal time from UTC+0 to UTC+1. Decree No. 25/2017, published in the Diário da República on December 28, ordered the change for the entire national territory from January 1, 2018.

The decree is unusually revealing about its reasoning. Its preamble says that São Tomé and Príncipe had retained Greenwich Mean Time after independence but considered that choice unsuitable when compared with apparent solar time. The text then discusses true solar time and solar noon before stating that local time should be adjusted toward it.

The mechanism was exact. At 01:00 on January 1, every clock was to be advanced by sixty minutes, making the next displayed time 02:00. IANA consequently recorded the transition from UTC+0 to UTC+1 at that boundary. This was not a seasonal daylight-saving program: the decree created a new legal offset without specifying a summer and winter cycle.

One clause sits oddly beside the one-hour advance. For international contractual and commercial relations, the decree continued to designate the Greenwich meridian as fundamental throughout the country. The same law therefore moved domestic legal time away from UTC while explicitly preserving Greenwich as a reference for certain international dealings.

The experiment lasted through the whole of 2018. There was no spring or autumn clock change and no attempt to repeat the arrangement seasonally.

At 02:00 on New Year's Day 2019, the Hour from 01:00 to 01:59 Happened Again

The reversal was legislated before the year was over. Decree No. 34/2018, published on December 11, restored the country's legal time to Coordinated Universal Time from January 1, 2019. The transition was specified for 02:00 while the country was still on UTC+1.

Clocks therefore moved backward from 02:00 to 01:00. Local times between 01:00 and 01:59 occurred twice that morning: once under UTC+1 before the change and again under UTC+0 afterward. A timestamp such as 01:30 on January 1, 2019 is ambiguous without the offset, because the two occurrences correspond to different UTC instants.

IANA incorporated the reversal in its December 2018 time-zone release, ending the UTC+1 period exactly where the new decree required. From the database's point of view, 2018 is a self-contained interruption in an otherwise long UTC+0 sequence.

The Time Restored in 2019 Had Been Written Into Colonial Law More Than a Century Earlier

Calling the 2019 change a restoration has a concrete historical basis. A Portuguese decree of May 24, 1911 established legal time across Portugal and its overseas territories according to the international meridian system adopted at Washington in 1884. For the territory of São Tomé and Príncipe, Article 2 prescribed a time identical to Greenwich.

The decree did not take effect there immediately. Article 5 ordered the new system to begin when January 1, 1912 started under the rules assigned to each territory, with clocks advanced or retarded as necessary. São Tomé and Príncipe consequently entered 1912 on Greenwich time while still under Portuguese colonial administration.

Decades later, the preamble to the independent country's 2017 decree explicitly acknowledged that GMT had been retained after independence. The one-hour move of 2018 was therefore a break with a clock regime whose legal roots on the islands reached back to the beginning of 1912; Decree No. 34/2018 restored that UTC-based regime one year later.

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