Three date-math questions, one calculator
"Difference" answers how far apart are these two dates: pick a start and end date and it returns the exact day count plus a years/months/days breakdown. "Shift date" answers what date is N days from this one, the calculation behind every "30 days from today," "90 days from today," or "45 days before this date" search. "Days until" answers a narrower, very common question on its own: a live countdown to the next New Year's Day, Halloween, Thanksgiving, and Christmas, automatically rolling to next year the moment each one passes.
All three share the same underlying date arithmetic, so switching modes never produces a different answer for the same pair of dates: "Difference" from today to next Christmas and "Days until → Christmas" always agree.
Total days and the years/months/days breakdown can tell different stories
The "Total days" figure is unambiguous: a straight count of calendar days between two dates, the same number you would get counting boxes on a calendar. The "Calendar span" (Ny Nm Nd) figure is a different, more human convention: it answers "how many full years, then full months, then full days" separate the two dates, the way people describe an age or an anniversary.
These two can diverge by exactly one day in a specific, well-documented edge case: an anniversary of February 29 measured against February 28 in a non-leap year. From Feb 29, 2024 to Feb 28, 2025 is 365 total days, but the calendar breakdown reads 11 months and 30 days, not a clean 1 year, because the month-and-day pair (Feb, 28) has not yet reached (Feb, 29), the same "has the anniversary date been reached" rule Microsoft documents for Excel's DATEDIF function. A different, equally common convention (used by Python's dateutil library, among others) instead clamps to the nearest valid day and calls that same pair exactly 1 year: there is no single universal answer for this specific edge case, only different documented rules for handling a date that does not exist in the target year.
Why "N days from today" has to be calculated live
A search like "30 days from today" or "90 days from today" does not have one fixed answer; it depends entirely on what day it is when you ask. The "Shift date" mode defaults to today's date (read from your browser) plus 30 days specifically so the calculator is useful the instant it loads, and the "Days until" mode works the same way: it reads today's date locally and calculates each holiday's distance from there, with no server round-trip and no risk of showing yesterday's countdown.
The reference table below shows what these additions look like from one fixed anchor date (January 1, 2026) instead of "today," so the worked examples stay accurate no matter when you read this page. Enter your own start date in the calculator above for a live answer.
Where the fourth Thursday of November comes from
Christmas (December 25), Halloween (October 31), and New Year's Day (January 1) are fixed calendar dates that need no calculation: they land on the same month and day every year. Thanksgiving in the United States is different: it is defined not by a fixed date but by a rule. A 1941 joint resolution of Congress, now codified at 5 U.S.C. § 6103, fixes Thanksgiving as "the fourth Thursday in November," which is why it moves around the calendar (November 22 through 28) from year to year while always landing on the same weekday. This calculator applies that rule directly rather than looking up a stored date, so it works correctly for any year.