date_when: Calculate and display date of specific pregnancy week

In pregnancy: Calculate and Track Dates and Medications During Pregnancy

Calculate and display date of specific pregnancy week

Description

Calculate and display date of specific pregnancy week

Usage

date_when(weeks, due_date = NULL, person = NULL, today = Sys.Date())

Arguments

weeks	Numeric value indicating the number of weeks of pregnancy to calculate the date for.
due_date	Date or character string representing a date, e.g. "YYYY-MM-DD". The expected due date. If NULL, will try to use the "pregnancy.due_date" option. Required if option not set.
person	The person who is pregnant, to determine the grammar for the output message. Can be: "I", "1", "1st", "first", or numeric 1 for first person "you", "2", "2nd", "second", or numeric 2 for second person Any other name for third person NULL: will try to use the "pregnancy.person" option. Defaults to "You" if the option is set.
today	Date or character string representing a date, e.g. "YYYY-MM-DD". Represents the reference date for calculations. Default is Sys.Date(). This parameter exists primarily for testing and documentation purposes and it is unlikely to make sense for the user to need or want to change it from the default.

Details

The function calculates when someone will be/was a specific number of weeks pregnant based on their due date. It handles past, present and future dates appropriately in its messaging. The due date can be provided directly or set globally using options("pregnancy.due_date"). Similarly, the person being referenced can be provided directly or set globally using options("pregnancy.person").

If date_when or today is a character string, the conversion to a Date is handled by anytime::anydate().

Value

Invisibly returns a Date object of when the specified week of pregnancy occurs/occurred/will occur.

Prints messages to the console showing:

• When the specified week of pregnancy occurs/occurred/will occur

• How far in the past/future that date is from today (unless that date is the current date)

See Also

calculate_due_date() for calculating the due date set_due_date() for setting the due date as a global option how_far() for calculating current pregnancy progress

Examples

# Set a due date
date_when(20, due_date = "2025-12-01")
date_when(33, due_date = as.Date("2025-12-01"), person = "Sarah")

pregnancy documentation built on Sept. 14, 2025, 5:09 p.m.