What does Is Leap Day do that other Date & time pages on this site do not?

leapDay is 1 only on Feb 29. leapYear is 1 for Gregorian leap years even if the date is not Feb 29. Short version: Leap-day flag plus leap-year flag.

Does Is Leap Day upload my file or text to Tool-You servers?

No. Is Leap Day runs in this browser tab. Files stay on the device. Limit note: Gregorian leap rules. Local YMD.

Should I use Leap Year Check instead of Is Leap Day?

Use Is Leap Day when you need Leap-day flag plus leap-year flag. Use Leap Year Check when you need Is leap year? Plus next/previous leap years. They share a category (Date & time) but not the same job.

Is Leap Day

Leap-day flag plus leap-year flag.

leapDay is 1 only on Feb 29. leapYear is 1 for Gregorian leap years even if the date is not Feb 29.

What Is Leap Day does

leapDay is 1 only on Feb 29. leapYear is 1 for Gregorian leap years even if the date is not Feb 29.

Is Leap Day sits in the Date & time group on purpose. It is not Leap Year Check (Is leap year? Plus next/previous leap years.) and not Days in Year (365 or 366 for a year.). Choose this page when you need Leap-day flag plus leap-year flag. If you stretch Is Leap Day into a neighbor’s job, the result will look wrong even though the site chrome looks the same.

How to use Is Leap Day

Confirm you need Is Leap Day, not Leap Year Check (Is leap year? Plus next/previous leap years.). Address: /datetime/is-leap-day.
Enter the numbers or dates Is Leap Day uses. Leap-day flag plus leap-year flag.
Read the result as Is Leap Day defines it — not as Days in Year (365 or 366 for a year.). leapDay is 1 only on Feb 29. leapYear is 1 for Gregorian leap years even if the date is not Feb 29.
Is Leap Day is an estimate in the browser, not professional advice. Gregorian leap rules. Local YMD.
Need a different formula? Try Days in Year (365 or 366 for a year.) instead of stretching Is Leap Day.

When not to use Is Leap Day

Skip Is Leap Day when a neighbor tool matches better — start with Leap Year Check or Days in Year — or when the description already warns the job will fail. In the tool’s own words: leapDay is 1 only on Feb 29. leapYear is 1 for Gregorian leap years even if the date is not Feb 29.

Questions about Is Leap Day

What does Is Leap Day do that other Date & time pages on this site do not?: leapDay is 1 only on Feb 29. leapYear is 1 for Gregorian leap years even if the date is not Feb 29. Short version: Leap-day flag plus leap-year flag.
Does Is Leap Day upload my file or text to Tool-You servers?: No. Is Leap Day runs in this browser tab. Files stay on the device. Limit note: Gregorian leap rules. Local YMD.
Should I use Leap Year Check instead of Is Leap Day?: Use Is Leap Day when you need Leap-day flag plus leap-year flag. Use Leap Year Check when you need Is leap year? Plus next/previous leap years. They share a category (Date & time) but not the same job.
What are the limits of Is Leap Day?: Gregorian leap rules. Local YMD. Also: leapDay is 1 only on Feb 29. leapYear is 1 for Gregorian leap years even if the date is not Feb 29.