Day of Week Calculator
Find day of the week (Monday-Sunday) for any calendar date.
Date Add / Subtract Calculator
About Day of Week Calculator
The Day of the Week & Historical Date Calculator determines the exact day of the week (Monday through Sunday) for any past, present, or future date using Zeller's Congruence algorithm, Julian-to-Gregorian transition rules, and day of year metrics.
How to Use Day of Week Calculator
Step 1
Pick a date from the calendar picker or type any historical/future date.
Step 2
Review computed Day of the Week, Day of Year, and calendar metrics.
Step 3
Click "Copy Day of Week".
Practical Use Cases for Day of Week Calculator
Historical Research & Genealogical Ancestry Fact-Checking
Verify the historical day of the week for historical treaties, battles, birth records, and marriage certificates across centuries.
Event Planning & Recurring Annual Anniversary Scheduling
Calculate what day of the week upcoming birthdays, corporate product launches, and holidays will land on in future years.
Input & Output Examples
Finding Day of Week for July 20, 1969 (Apollo 11 Moon Landing)
Date: `July 20, 1969`
Day of Week: `Sunday` | Day of Year: `201` | ISO Week: `Week 29` | Leap Year: `No (365 days)`
Key Features & Performance
- ✓Zeller's Congruence Engine: computes exact day of the week for any Gregorian calendar date from year 1 AD to 9999 AD.
- ✓Comprehensive Date Stats: calculates Day of the Year ($1-366$), ISO Week Number ($1-53$), Quarter, and Days Remaining in Year.
- ✓Multi-Language Day Names: displays day name in English, Spanish, French, German, Japanese, Chinese, and Hindi.
- ✓100% Client-Side memory execution.
- ✓1-Click Copy day of week summary.
Key Terminology & Definitions
Zeller's Congruence
An algorithm devised by Christian Zeller to calculate the day of the week for any Julian or Gregorian calendar date ($h = (q + \lfloor 13(m+1)/5 \rfloor + K + \lfloor K/4 \rfloor + \lfloor J/4 \rfloor - 2J) \pmod 7$).
Day of Year (Ordinal Date)
The sequential day number of a date within a calendar year, ranging from 1 (January 1st) to 365 (or 366 in leap years).