Day of the Week Calculator

Bulk Check (Optional)

Drag & drop a .txt or .csv with one date per line (YYYY-MM-DD), or choose a file .

Nothing is uploaded—processed locally in your browser.

Input: one YYYY-MM-DD date.
Weekday name is derived from calendar rules; ISO weekday numbers are Mon=1 … Sun=7.
ISO week of year uses ISO-8601: weeks start on Monday; week 1 is the week with the year’s first Thursday.
Day of year runs 1–365/366 (leap years accounted for automatically).
Parsing: strict UTC to avoid DST/timezone drift; invalid formats are rejected.
Bulk mode: paste/drag multiple lines or load a file; each line parsed as YYYY-MM-DD.

Common pitfalls

Ensure leading zeros: use 2025-03-07, not 2025-3-7.
Excel may reformat dates on export; save as plain text (UTF-8) to preserve YYYY-MM-DD.
If a line is blank or malformed, it will be flagged and skipped in bulk mode.