Description
Convert between ISO weekday numbering and Sunday-zero numbering.
Civil calendar arithmetic needs explicit year numbering, leap rules and index origins. A weekday mask or Gregorian component operation does not identify a timezone, working calendar or historical calendar reform.
Convert between ISO weekday numbering and Sunday-zero numbering.
When to use this tool
Use ISO Weekday Sunday Zero Crosswalk when checking the stated weekday or Gregorian calendar convention.
How to use the tool and how it works
- Enter day, fromIso. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read day. Use the output convention below.
Convert between ISO weekday numbering and Sunday-zero numbering. Require ISO 1-7 or Sunday-zero 0-6 according to fromIso; map Sunday between seven and zero.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| day | Day | Required. Safe integer. |
| fromIso | From Iso | Required. Boolean. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| day | Day | Required. Safe integer. |
{
"input": {
"day": 7,
"fromIso": true
},
"output": {
"day": 0
}
}Limitations and assumptions
- This changes numbering only and does not derive a weekday from a date.
- 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 an appropriate full calendar library and authoritative local rules when business days, historical dates or real scheduling matter.
References
Similar or alternative tools
- ISO Weekday Cycle Offset
Advance an ISO weekday by a signed day offset with week carry.
- Date: Weekday Mask Bitset Label
Decode a seven-bit weekday mask to labels.