This is an R package for calculating dates and tracking medications during pregnancy and fertility treatment. It extends a private, personal package that I wrote for myself when I was pregnant. It contains functions and features that I found useful at the time, and others that I added when adapting the package for general use.
The functionality goes beyond what’s offered by online pregnancy calculators and apps, plus there are no concerns (unlike with these sites and apps) about data privacy, tracking or advertising.
The pregnancy package uses dates extensively. Any
function argument that requires a date can either take a
Date object1, or a character string that can be parsed
to a Date, e.g. "YYYY-MM-DD". The parsing is
performed by anytime::anydate().
The calculate_due_date() function estimates the
pregnancy due date. The start_date is interpreted
differently, depending on the start_type. By default, the
start_type is the last menstrual period, and the
start_date is the date this started. Other
start_date options, like various transfer days, are useful
for those using IVF.
# invisibly returns a Date object with the estimated due date
due_date <- calculate_due_date("2025-02-24")
#> ℹ Estimated due date: Monday, December 01, 2025
#> ℹ Estimated birth period begins: November 10, 2025 (37 weeks)
#> ℹ Estimated birth period ends: December 15, 2025 (42 weeks)Once a due date is know, how_far() tells you how far
along the pregnancy is on a given date. It defaults to providing this
information for the current date, but an alternative
on_date can be provided. This vignette was built on
September 09, 2025, so for the purposes of reading this
article, that counts as “today”.
how_far(due_date = due_date)
#> ℹ You are 28 weeks and 1 day pregnant.
#> ℹ That's 11 weeks and 6 days until the due date (December 01, 2025).
#> ℹ You are 70% through the pregnancy.
how_far(on_date = "2025-09-17", due_date = due_date)
#> ℹ On September 17, 2025, you will be 29 weeks and 2 days pregnant.The date_when() function gives the date when a certain
week of pregnancy will be (or was) reached, and the duration of that
date from today:
date_when(33, due_date = due_date)
#> ℹ On October 13, 2025, you will be 33 weeks pregnant.
#> ℹ That's 4 weeks and 6 days away.By default, the output messages from how_far() and
date_when() are in the second person, i.e. addressed to
“you”, but there is also an option to specify another person. A value of
1 or "I" means you’ll be addressed in the
first person:
how_far(due_date = due_date, person = 1)
#> ℹ I am 28 weeks and 1 day pregnant.
#> ℹ That's 11 weeks and 6 days until the due date (December 01, 2025).
#> ℹ I am 70% through the pregnancy.Any other character string will be interpreted as a third-person name, which is useful, for example, if you’re following the pregnancy progress of a partner:
date_when(33, due_date = due_date, person = "Ruth")
#> ℹ On October 13, 2025, Ruth will be 33 weeks pregnant.
#> ℹ That's 4 weeks and 6 days away.There is one further date-related function in the package, which is
useful if you are not yet pregnant but think there’s a chance you might
be, e.g. if you are undergoing fertility treatment. This is
calculate_test_date(), which calculates the recommended
date for taking a pregnancy test, based on start date (e.g. start of
last menstural period) and test type:
For those who get pregnant via fertility treatment, it is likely they
need to take a number of different medications to support the pregnancy.
Having functionality for tracking these is useful for both practical and
emotional reasons. When I was pregnant, in my personal, private
pregnancy package, whenever I called my version of how_far,
it would print a message with how many injections I had already endured,
and how many I had left to go, which helped me get through them.
I haven’t written that functionality into how_far() in
this generalised version of the pregnancy package, but I have provided a
separate medications_remaining() function to keep track of
medications. It requires a data frame of medications, which must have
the following columns with the specified data types:
| Column name | Data type | Description |
|---|---|---|
| medication | character or factor | name of the medication |
| format | character or factor | format of the medication (e.g. pill, injection) |
| quantity | numeric | number of units to take per day |
| start_date | Date or string representing a date, e.g. “YYYY-MM-DD” | date to start taking the medication |
| stop_date | Date or string representing a date, e.g. “YYYY-MM-DD” | final date on which medication is taken |
Note that if the quantity of a given medication changes during the pregnancy, you need separate rows with the start and stop dates for each quantity.
Here’s an example of what a small medications table
might look like (a larger example table is provided in the package as
pregnancy::medications):
# a simplified medication schedule
meds <- dplyr::tribble(
~medication, ~format, ~quantity, ~start_date, ~stop_date,
"progynova", "tablet", 3, "2025-08-21", "2025-08-31",
"progynova", "tablet", 6, "2025-09-01", "2025-09-11",
"cyclogest", "pessary", 2, "2025-09-03", "2025-09-11",
"clexane", "injection", 1, "2025-09-08", "2025-11-05"
)You can then calculate the quantity of medications left to take
grouped by either by medication (default) or format. By default, the
calculation is for today (i.e. on_date =
Sys.Date()). The resulting table assumes that the function
is being called first thing in the day, i.e. before any of
on_date’s medications have been taken.
medications_remaining(meds)
#> # A tibble: 3 × 2
#> medication quantity
#> <chr> <int>
#> 1 clexane 58
#> 2 cyclogest 6
#> 3 progynova 18medications_remaining(meds, group = "format")
#> # A tibble: 3 × 2
#> format quantity
#> <chr> <int>
#> 1 injection 58
#> 2 pessary 6
#> 3 tablet 18You can specify a value other than today for on_date, as
well as an until_date. This is useful if you need (as I
did) to order a couple of week’s medication at the time, and have to
tell the pharmacy exactly what you need:
It would be very tedious to have to enter a due date every time you
call how_far() or date_when() over the course
of a pregnancy, especially since that date is constant throughout. The
same goes for the medications table required for
medications_remaining().
To avoid this, the pregnancy package makes use of global
options, which can be set with the set_* family of
functions (set_due_date(), set_person(),
set_medications()). These functions only set the options
for the current R session.
To ensure the options persist across all R sessions, we suggest
setting them in your .Rprofile, and give an example at the
end of this vignette.
Global options can be retrieved with the get_* family of
functions (get_due_date(), get_person(),
get_medications()).
Any global option can be unset by calling its set_*
function with the argument NULL.
pregnancy.due_dateYou can set the pregnancy.due_date option using the
set_due_date() function.
When that option is set, if the due_date argument to
how_far() or date_when() is NULL
(the default), that option is retrieved.
set_due_date() only sets the due date for the current R
session. To make this option persist (recommended), it can be added to
your .Rprofile. The console output of
set_due_date() provides guidance on how to do this.
# can be intentional about creating a Date object
due_date <- as.Date("2026-01-22")
set_due_date(due_date)
#> ✔ Due date set as January 22, 2026
#> ℹ Functions in the pregnancy package will now use this `due_date` option.
#> ℹ So, for this R session, you do not need to supply a value to the `due_date`
#> argument (unless you wish to override the option).
#> ℹ To make this `due_date` option available in all R sessions, in your
#> ".Rprofile", set `options(pregnancy.due_date = ...)`
#> where ... is the value of `due_date`.
#> ℹ You can edit your ".Rprofile" by calling `usethis::edit_r_profile()`
#> ℹ You can retrieve the `due_date` option with `get_due_date()`,
#> or with `getOption('pregnancy.due_date')`.Then how_far() can be called without needing to specify
any arguments, and date_when() only needs the target
week:
how_far()
#> ℹ You are 20 weeks and 5 days pregnant.
#> ℹ That's 19 weeks and 2 days until the due date (January 22, 2026).
#> ℹ You are 52% through the pregnancy.To check what the option is set to, use
get_due_date().
pregnancy.personset_person() sets the global option
pregnancy.person for the current R session. If this option
is set it will be retrieved to specify the value of person
in how_far() and date_when(), unless it is
overriden by passing another value directly to the person
argument. If the option is not set, the default second-person will be
used.
set_person(1)
#> ✔ person set as 'I'
#> ℹ Functions in the pregnancy package will now use this `person` option.
#> ℹ So, for this R session, you do not need to supply a value to the `person`
#> argument (unless you wish to override the option).
#> ℹ To make this `person` option available in all R sessions, in your
#> ".Rprofile", set `options(pregnancy.person = ...)`
#> where ... is the value of `person`.
#> ℹ You can edit your ".Rprofile" by calling `usethis::edit_r_profile()`
#> ℹ You can retrieve the `person` option with `get_person()`,
#> or with `getOption('pregnancy.person')`.
how_far() # due_date option still set from previous section
#> ℹ I am 20 weeks and 5 days pregnant.
#> ℹ That's 19 weeks and 2 days until the due date (January 22, 2026).
#> ℹ I am 52% through the pregnancy.
set_person(NULL)
#> ✔ pregnancy.person option set to NULL.
#> ℹ The `person` argument will now default to "You".
how_far()
#> ℹ You are 20 weeks and 5 days pregnant.
#> ℹ That's 19 weeks and 2 days until the due date (January 22, 2026).
#> ℹ You are 52% through the pregnancy.pregnancy.medicationsset_medications() sets the global option
pregnancy.medications for the current R session.
When that option is set, if the meds argument to
medications_remaining() is NULL (the default),
that option is retrieved.
set_medications(pregnancy::medications)
#> ✔ medications set.
#> ℹ Functions in the pregnancy package will now use this `medications` option.
#> ℹ So, for this R session, you do not need to supply a value to the
#> `medications` argument (unless you wish to override the option).
#> ℹ To make this `medications` option available in all R sessions, in your
#> ".Rprofile", set `options(pregnancy.medications = ...)`
#> where ... is the value of `medications`.
#> ℹ You can edit your ".Rprofile" by calling `usethis::edit_r_profile()`
#> ℹ You can retrieve the `medications` option with `get_medications()`,
#> or with `getOption('pregnancy.medications')`.
medications_remaining()
#> # A tibble: 5 × 2
#> medication quantity
#> <chr> <int>
#> 1 clexane 88
#> 2 cyclogest 66
#> 3 lubion 33
#> 4 prednisolone 153
#> 5 progynova 198.RprofileTaking the advice to specify the options in your
.Rprofile, here’s an example of what that might look
like:
options(
pregnancy.due_date = "2025-09-16",
pregnancy.person = "I", # addressed in first person
pregnancy.medications = dplyr::tribble(
~medication, ~format, ~quantity, ~start_date, ~stop_date,
"progynova", "tablet", 3, "2025-04-21", "2025-04-30",
"progynova", "tablet", 6, "2025-05-01", "2025-07-11",
"cyclogest", "pessary", 2, "2025-05-03", "2025-07-11",
"clexane", "injection", 1, "2025-05-08", "2025-09-05"
)
)Note that it is best to avoid creating R objects in your
.Rprofile, e.g. a medications data frame
outside of the call to options(), otherwise that object
will be loaded into your global environment at the start of every R
session.
There are many ways to create Date objects
in R, including as.Date(), lubridate::ymd(),
and anytime::anydate().↩︎