Description
Return signed month offset from a supplied year-month origin.
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.
Return signed month offset from a supplied year-month origin.
When to use this tool
Use Month Index Relative Origin when checking the stated weekday or Gregorian calendar convention.
How to use the tool and how it works
- Enter year, month, originYear, originMonth. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read monthOffset. Use the output convention below.
Return signed month offset from a supplied year-month origin. Require months in [1,12]; compute (year-originYear)*12+month-originMonth using exact integer intermediate arithmetic.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| year | Year | Required. Safe integer. |
| month | Month | Required. Safe integer; minimum 1; maximum 12. |
| originYear | Origin Year | Required. Safe integer. |
| originMonth | Origin Month | Required. Safe integer; minimum 1; maximum 12. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| monthOffset | Month Offset | Required. Safe integer. |
{
"input": {
"year": 2026,
"month": 3,
"originYear": 2025,
"originMonth": 11
},
"output": {
"monthOffset": 4
}
}Limitations and assumptions
- The offset describes calendar-month coordinates, not elapsed days; output numeric bounds still apply.
- 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
- Weekday Occurrence Remaining In Month
Return a date's ordinal occurrence of its weekday within its month and later occurrences.
- Calendar Month Ordinal Serial Pair
Return a serial month coordinate.