Description
Format valid supplied ISO week-year, week and weekday fields.
Date formats distinguish calendar years from ISO week-years, known day precision from unknown-day masks, and midnight at the start versus end of a day. A fixed 86400-second day fraction does not encode civil timezone transitions. Partial-date wording preserves uncertainty rather than silently choosing a date.
Format valid supplied ISO week-year, week and weekday fields.
When to use this tool
Use ISO Week Date Field Formatter when you already have weekYear, week, weekday and need to format valid supplied ISO week-year, week and weekday fields.
How to use the tool and how it works
- Enter weekYear, week, weekday. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read weekDate. Use the output convention below.
Require weekYear 0000..9999, week 1..53 and weekday 1..7. Week 53 is permitted only when January 1 is Thursday or Wednesday in a leap year. Return YYYY-Www-d with padded year/week.1
ISO week 1 includes the year's first Thursday, and its week-year can differ from the civil year near New Year. The supplied week-year must therefore be retained rather than replaced with a calendar year.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| weekYear | ISO week-year from 0000 through 9999; can differ from the civil calendar year. | Required. Safe integer; minimum 0; maximum 9999. |
| week | Week | Required. Safe integer; minimum 1; maximum 53. |
| weekday | ISO whole weekday 1=Monday through 7=Sunday. | Required. Safe integer; minimum 1; maximum 7. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| weekDate | Week Date | Required. Text; maximum UTF-16 length 8192. |
{
"input": {
"weekYear": 2026,
"week": 44,
"weekday": 7
},
"output": {
"weekDate": "2026-W44-7"
}
}Limitations and assumptions
- The week-year can differ from the calendar year near New Year. No civil date is converted, timezone resolved or astronomical/historical calendar interpretation added.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Use a complete calendar/timezone conversion when relating week dates, timestamps or local schedules. Preserve unknown precision explicitly and choose an endpoint policy before calculation; a formatter or fixed-day fraction does not resolve missing dates or civil-time rules.
References
Similar or alternative tools
- End Of Month Unknown Day Mask
Format a supplied civil month with either a validated day or an unknown-day mask.
- Civil Day Fraction Midnight Policy
Convert a supplied clock to a fixed 24-hour day fraction with an end-of-day policy.