ISLEAPYEAR in Collabora Office: Check the Year of a Valid Date
Use Collabora ISLEAPYEAR with real dates, audit century exceptions and avoid treating a typed year or date-like division as a date.
Verification status: See the evidence and test scope described in this guide. How formula examples are checked
Quick answer: =ISLEAPYEAR(DATE(2024;1;1)) has independently expected result 1 (TRUE). A date in 2025 targets 0 (FALSE). The argument is a date belonging to the year being tested.
Syntax and result type
=ISLEAPYEAR(Date)
Date is the one required valid date. The dedicated Collabora help explicitly describes 1 for a leap year and 0 otherwise. It documents a DATE-based February 29, 1968 example.
This function tests the year containing the date. It does not validate whether a typed day/month combination was originally legitimate before another function normalized it. Use a known valid date such as January 1 when your input is just a year number.
The modern Gregorian rule used for the independent controls is divisibility by four, except century years must also be divisible by 400. That rule explains the century examples below.
Example 1: build a leap-year check
Enter 2023, 2024, 2000, 2100 in A2:A5 as year numbers. In B2 enter =DATE(A2;1;1) and fill down. In C2 use =ISLEAPYEAR(B2) and fill down.
Independent expected outputs are 0, 1, 1, 0. Year 2000 passes the 400-year condition; 2100 is divisible by 100 but not 400.
The extra date-construction column is deliberate. Passing A2 directly to ISLEAPYEAR would pass a serial date number, not the intended year field. Keeping B visible makes that conversion auditable.
Example 2: verify against February’s length
For each B2:B5 date, calculate =DAYSINMONTH(DATE(YEAR(B2);2;1)) in D2 and fill down. Independent February lengths are 28, 29, 29, 28.
The expression =D2=29 should agree with the leap-year flag for these controls. A different result suggests a wrong year or a formula-reference error. It does not prove that every other cell in a larger calendar table is correct.
Advanced application: create a readable label
Use =IF(ISLEAPYEAR(B2);"Leap year";"Common year") in a display column. For a year-level calendar denominator, =365+ISLEAPYEAR(B2) independently targets the same count as DAYSINYEAR(B2) for these modern Gregorian examples.
Keep the Boolean/numeric flag if later formulas need it, and use a separate text label for readability. Converting the flag to a text phrase and then relying on implicit numeric conversion complicates downstream calculations.
Advanced application: distinguish date construction from validation
Constructing DATE(year;2;29) is not a safe way to test whether February 29 is valid for that year. Spreadsheet date constructors can normalize an out-of-range day into another month. ISLEAPYEAR then evaluates the year of the resulting date, not the original typed assertion.
For a leap-year test from a year field, construct January 1 as above. If validating imported date text, first preserve the original text and apply an explicit parsing/validation rule; a leap-year flag alone is insufficient.
Historical compatibility and input errors
The official source warns about Excel’s treatment of the nonexistent February 29, 1900 and differences in dates before March 1, 1900. Do not assume a numeric date serial imported from another application identifies the same historical date without checking the date system.
The help also warns that =ISLEAPYEAR(2/29/68) evaluates arithmetic division before interpreting the small result as a date serial. Use DATE(1968;2;29) or an already valid date cell instead.
Exact native invalid-date error displays, historical conversions and timestamp handling were not executed here. The worked controls use explicit valid modern dates and independent Gregorian calculations.
Availability, format and verification
Collabora Office 26.04 desktop help documents this exact function. The saved source was retrieved on 2026-10-13 and hash-verified for this guide on October 15, 2026. It identifies the namespace ORG.OPENOFFICE.ISLEAPYEAR and says the function is outside the cited OpenFormula 1.3 standard. This is not cross-product semantic certification.
The first introduced release and last functioning version are unknown. Online/mobile availability is not inferred. No native Collabora or WPS execution was performed. Results are independent calendar/string controls or explicitly identified documented examples. English names and semicolon separators are used.