Days and Dates

Library with some basic functions to enable math with dates and days following ISO 8601. Functions return datestamps (Number of days since 1st January 0000). A week begins on Monday Check the test/daydate.l4 file to see examples or play around with it in our online-editor.

Here are some example on how to use it:

IMPORT daydate

#EVAL `is leap year` 2400                                 -- TRUE - Century divisible by 400
#EVAL Feb 29 2000 EQUALS Day (Date 29 2 2000)             -- TRUE - leap day
#EVAL Week 53 2009 EQUALS Dec 28 2009                     -- TRUE - Last week of 53-week year
#EVAL Jan 1 2000 MINUS 1 EQUALS Dec 31 1999               -- TRUE - Subtraction across millennium
#EVAL `Weekday of 1st day of month` 3 2025 EQUALS Saturday-- TRUE - First day of month
#EVAL `the earlier of` (Feb 29 2024) (Feb 28 2024)        -- 739308 - Earlier in leap month

Constants

Time Periods

• Months in a year: 12

• Days in a year: 365.2425 (accounts for 4-year leap cycle with 100 and 400 year exceptions)

• Days in a month: 30.436875 (average month length)

• Days in a week: 7

Month & Weekday Constants

Following ISO standard with January 1, 0000 being a Sunday:

Weekday	Alias	Value
Monday	Mon	1
Tuesday	Tue	2
Wednesday	Wed	3
Thursday	Thu	4
Friday	Fri	5
Saturday	Sat	6
Sunday	Sun	0

Month	Alias	Value
January	Jan	1
February	Feb	2
March	Mar	3
April	Apr	4
May		5
June	Jun	6
July	Jul	7
August	Aug	8
September	Sep	9
October	Oct	10
November	Nov	11
December	Dec	12

Date Constructors

Date AKA Days to date (from components)

Creates a DATE object from day, month, and year components.

• Given:

  • day: NUMBER (day of month)

  • month: NUMBER (month number 1-12)

  • year: NUMBER (4-digit year)

• Giveth: DATE object with day, month, and year properties

Date AKA Days to date

Converts a datestamp into a DATE object.

• Given:

  • days: NUMBER datestamp or DATE object

• Giveth: DATE object with day, month, and year properties

Datestamp Constructors

Day AKA Date to days (from components)

Creates a datestamp from day, month, and year.

• Given:

  • day: NUMBER (day of month)

  • month: NUMBER (month number 1-12)

  • year: NUMBER (4-digit year)

• Giveth: NUMBER datestamp

Day AKA Date to days (from date)

Converts a DATE object to a datestamp.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

Year (from year)

Creates a datestamp for the first day of a given year.

• Given:

  • year: NUMBER (4-digit year)

• Giveth: NUMBER datestamp

Year (from date)

Creates a datestamp for the first day of a year from a DATE object.

• Given:

  • date: DATE object

• Giveth: NUMBER datestamp

Month (from components)

Creates a datestamp for the first day of a month.

• Given:

  • month: NUMBER (month number 1-12)

  • year: NUMBER (4-digit year)

• Giveth: NUMBER datestamp

Month (from date)

Creates a datestamp for the first day of a month from a DATE object.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

Week (from components)

Creates a datestamp for the first day of a week a given week and year (Monday).

• Given:

  • week: NUMBER (week number)

  • year: NUMBER (4-digit year)

• Giveth: NUMBER datestamp

Week (from date)

Creates a datestamp for the first day of a week (Monday) for a given date.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

Month Helpers

The following functions create datestamps within specific months. Each takes a day and year and returns a datestamp. E.g. January 1 2025 -> 20088

• January (AKA Jan)

• February (AKA Feb)

• March (AKA Mar)

• April (AKA Apr)

• May

• June (AKA Jun)

• July (AKA Jul)

• August (AKA Aug)

• September (AKA Sep)

• October (AKA Oct)

• November (AKA Nov)

• December (AKA Dec)

• Given:

  • day: NUMBER (day of month)

  • year: NUMBER (4-digit year)

• Giveth: NUMBER datestamp

Month of the year

Gets the month number of a given date.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER (month number, e.g. 2 for February)

Datestamp Math Helpers

Months since year start to days (from components)

Calculates total days from start of year to beginning of a given month.

• Given:

  • month: NUMBER (month number 1-12)

  • year: NUMBER (4-digit year)

• Giveth: NUMBER (amount of days)

Months since year start to days (from date)

Calculates total number of days from start of year to a given month from a DATE object.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER (number of days)

Days in month (from components)

Gets the total number of days in a given month.

• Given:

  • month: NUMBER (month number 1-12)

  • year: NUMBER (4-digit year)

• Giveth: NUMBER (number of days)

Days in month (from date)

Gets the total number of days in a given month for a given date.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER (number of days)

Days in year (from year)

Calculates number of days in a given year.

• Given:

  • year: NUMBER (4-digit year)

• Giveth: NUMBER (365 or 366)

Days in year (from date)

Calculates number of days in a given year from a DATE object.

• Given:

  • date: DATE object

• Giveth: NUMBER (365 or 366)

Years to days (from year)

Calculates the total number of days from year 0 to a given year.

• Given:

  • year: NUMBER (4-digit year)

• Giveth: NUMBER (number of days)

Years to days (from date)

Calculates the total number of days from year 0 to a DATE objects year.

• Given:

  • date: DATE object

• Giveth: NUMBER (number of days)

Weekday Functions

Weekday of (from days)

Gets the weekday number (0-6) for a given date.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER (0-6)

Weekday of 1st day of month (from components)

Gets the weekday of the first day of a month.

• Given:

  • month: NUMBER (month number 1-12)

  • year: NUMBER (4-digit year)

• Giveth: NUMBER (0-6)

Weekday of 1st day of month (from date)

Gets the weekday of the first day of a month for a given date.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER (0-6)

Weekday of 1st day of year (from year)

Gets the weekday of January 1st of a given year. E.g. 2025 -> Wednesday

• Given:

  • year: NUMBER (4-digit year)

• Giveth: NUMBER (0-6)

Weekday of 1st day of year (from date)

Gets the weekday of January 1st from a DATE objects year.

• Given:

  • date: DATE object

• Giveth: NUMBER (0-6)

Week Functions

Week of the year

Gets the week of the year number for a given date.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER (week number)

Weeks in year (from year)

Calculates number of weeks in a given year. E.g. 2004 -> 53

• Given:

  • year: NUMBER (4-digit year)

• Giveth: NUMBER (52 or 53)

Weeks in year (from date)

Calculates number of weeks in a given year from a DATE object.

• Given:

  • date: DATE object

• Giveth: NUMBER (52 or 53)

Attribute Checkers

is weekend

Checks if a given date falls on a weekend.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: BOOLEAN

is weekday

Checks if a given date falls on a weekday.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: BOOLEAN

is leap year (from year)

Checks if a given year is a leap year. E.g. 2004 -> TRUE

• Given:

  • year: NUMBER (4-digit year)

• Giveth: BOOLEAN

is leap year (from date)

Checks if a given date's year is a leap year.

• Given:

  • date: DATE object

• Giveth: BOOLEAN

Relative Time Phrases

on day

Gets the date for the nth day of a given date. e.g. #EVAL Date (`on day` 2 (`the week after` (Jan 2 2026))) -> DATE OF 6, 1, 2026

• Given:

  • day: NUMBER (nth day, 1 being the same day)

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

the day after

Gets the date for the day AFTER a given date.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

the day before

Gets the date for the day BEFORE a given date.

• Given:

  • days: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

the week after

Gets the date for Monday of NEXT week from a given date.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

the week before

Gets the date for Monday of the PREVIOUS week from a given date.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

the month after

Gets the date for the first day of NEXT month.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

the month before

Gets the date for the first day of the PREVIOUS month.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

the year after

Gets the date for the first day of NEXT year.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

the year before

Gets the date for the first day of the PREVIOUS year.

• Given:

  • date: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

Comparators

the earlier of

Returns the earlier of two dates.

• Given:

  • date1: NUMBER datestamp or DATE object

  • date2: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

the later of

Returns the later of two dates.

• Given:

  • date1: NUMBER datestamp or DATE object

  • date2: NUMBER datestamp or DATE object

• Giveth: NUMBER datestamp

Stringify Functions

Name of month

Converts a datestamp to month name. (e.g. January)

• Given:

  • days: NUMBER datestamp or DATE object

• Giveth: STRING (month name)

Name of weekday

Converts a datestamp to weekday name. (e.g. Monday)

• Given:

  • days: NUMBER datestamp or DATE object

• Giveth: STRING (weekday name)