Fortnight fields store the selection of a fortnight, a two-week period.

For historical reasons, ActivityInfo uses the epidemiological week calendar, or “epi week” used to report healthcare statistics, rather than the ISO week date system.

Fortnight numbering

An epidemiological week, commonly referred to as an epi week, is a standardized method of counting weeks to allow for the comparison of data year after year.

The epiweek begins on Sunday and ends on Saturday. The first epidemiological week of the year ends on the first Saturday of January, provided that it falls at least four or more days into the month. Therefore, the first epidemiological week may actually begin in December of the previous year.

The WHO and national health authorities regularly publish epi week calendars for reference.

ActivityInfo defines a fortnight as beginning on an odd-numbered Epiweek. The first few fortnights of 2024 are then:

  • 2024W1-W2
  • 2024W3-W4
  • 2024W5-W6
  • 2024W7-W8

Fortnight format

When entering a fortnight as a text, ActivityInfo uses the format “YYYYW0-W0”, for example “2023W1-W2” or “2020W31-32”.

Data entry

Desktop data entry

Fortnights can be entered either by typing the year and week number in the format “2023W1-W2”, or by selecting a data from the calendar. When selecting a date, the data entry field will be updated with the corresponding fortnight.


When importing, fortnight fields should be formatted as “YYYYW00-W00”


Weeks must be between the year 1000 CE and the year 9999 CE.

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