Section author: Laiton Hedley

Date Handling

Use the techniques on this page when you need to:

Calculate someone’s age from their date of birth.
Measure the number of days between two events (e.g., start and end of a study).
Add or subtract days from a date (e.g., scheduling a follow-up).
Extract the year, month, or day from a date for grouping or filtering.

Note

jamovi does not have a native Date data type at this time (one is planned). The functions below treat dates as text or integers and allow common date arithmetic to be performed via Computed Variables.

Two functions form the foundation of date handling in jamovi:

DATEVALUE(var) — converts a date string such as 2025-01-29 to an integer representing the number of days since 1 January 1970.
DATE(var) — performs the reverse: converts such an integer into a formatted date string.

The typical workflow is to convert a date to an integer, perform arithmetic on it, and then convert the result back to a date string. Both functions optionally accept a format string for non-standard date formats.

Table 37 Example date formatting
Day	`DATE(Day)`	`DATE(Day, "%d %m %Y")`	`DATE(Day, "%m/%d/%y")`
13	1970-01-13	13 01 1970	01/13/70
4197	1981-06-29	29 06 1981	06/29/81

Adding Days to a Date

Convert a date to an integer, add the number of days, then convert back:

Table 38 Adding 7 days to a date
Date	`DATEVALUE(Date)`	`DATEVALUE(Date) + 7`	`DATE(DATEVALUE(Date) + 7)`
2026-01-29	20482	20489	2026-02-05
2024-03-10	19792	19799	2024-03-17
2025-08-22	20322	20329	2025-08-29

Days Elapsed Between Two Dates

Subtract the start date integer from the end date integer:

Table 39 Computing days elapsed
StartDate	EndDate	`DATEVALUE(EndDate) - DATEVALUE(StartDate)`
2026-01-29	2026-02-15	17
2024-03-10	2024-04-11	32
2025-08-22	2024-04-11	-498

Extracting Year, Month, or Day

Use the SPLIT() function to extract parts of a date string. It splits text by a delimiter and returns the chunk at the specified position. Note that SPLIT() returns text — wrap with INT() if you need the result as a number for arithmetic.

Table 40 Extracting year, month, and day
Date	`SPLIT(Date, '-', 1)`	`SPLIT(Date, '-', 2)`	`SPLIT(Date, '-', 3)`
2026-01-29	2026	01	29
2024-03-10	2024	03	10
2025-08-22	2025	08	22

Composing a Date from Parts

Concatenate year, month, and day strings with - as a separator:

Table 41 Composing a date from parts
Year	Month	DayOfMonth	`Year + '-' + Month + '-' + DayOfMonth`
2026	01	29	2026-01-29
2024	03	10	2024-03-10
2025	08	22	2025-08-22