Week Number Calculator
Week Number is evaluated from Date. The calculation reports Week Number, Week Starts and Week Ends.
Results
About the Week Number Calculator
The calculator uses a multi formula configuration. Each reported value is read as a direct evaluation of the stored rules with the declared field formats and units.
Formula basis:
ISO week number: Find January 4th of the year → find preceding Monday → count weeks from that Monday to the target date.
Quarter: Month 1 - 3 = Q1, 4 - 6 = Q2, 7 - 9 = Q3, 10 - 12 = Q4.
Interpret the outputs in the order shown by the result fields. Optional inputs affect only the outputs that depend on those variables.
Formula & How It Works
The calculation applies the following relations exactly as recorded in the metadata: ISO week number: Find January 4th of the year → find preceding Monday → count weeks from that Monday to the target date. Quarter: Month 1 - 3 = Q1, 4 - 6 = Q2, 7 - 9 = Q3, 10 - 12 = Q4. Each output field is produced by substituting the supplied inputs into the relevant relation and then applying the declared rounding or text format.
Worked Examples
Example 1: January 1, 2025
Inputs
With Date = 2025-01-01 as the stated inputs, the result is Week Number = 1, Week Starts = 2024-12-30 and Week Ends = 2025-01-05. Each value corresponds to the declared output fields.
Example 2: July 4, 2025 (Independence Day)
Inputs
With Date = 2025-07-04 as the stated inputs, the result is Week Number = 27, Week Starts = 2025-06-30 and Week Ends = 2025-07-06. Each value corresponds to the declared output fields.
Example 3: Tax Day 2025 — April 15
Inputs
With Date = 2025-04-15 as the stated inputs, the result is Week Number = 16, Week Starts = 2025-04-14 and Week Ends = 2025-04-20. Each value corresponds to the declared output fields.
Example 4: Christmas Day 2025 — December 25
Inputs
With Date = 2025-12-25 as the stated inputs, the result is Week Number = 52, Week Starts = 2025-12-22 and Week Ends = 2025-12-28. Each value corresponds to the declared output fields.
Common Use Cases
- Find which week number a date falls in for project scheduling
- Determine start and end dates of a given week number
- Schedule quarterly reports using calendar week references