Description
Calculate a one-based calendar-day index relative to a supplied menstrual-cycle start.
Gynecological records connect dates, laterality, specimen sites, device lots and measurement-axis labels. A day index or axis permutation describes supplied record conventions without predicting physiology or verifying anatomy. Screening codes and recall wording require their original clinical source and context.
Calculate a one-based calendar-day index relative to a supplied menstrual-cycle start.
When to use this tool
Use Menstrual Cycle Day Index when checking the stated gynecological record, calendar index or measurement-order convention.
How to use the tool and how it works
- Enter cycleStartDate, observationDate. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read oneBasedDay, beforeCycleStart. Inspect beforeCycleStart before interpreting the associated values.
Parse real YYYY-MM-DD observation/cycle-start dates at UTC midnight. Return observation-minus-start days plus one, and beforeCycleStart when the difference is negative.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| cycleStartDate | Cycle Start Date | Required. Text; maximum UTF-16 length 8192. Real proleptic Gregorian YYYY-MM-DD; four-digit years 0000-9999 accepted. |
| observationDate | Observation Date | Required. Text; maximum UTF-16 length 8192. Real proleptic Gregorian YYYY-MM-DD; four-digit years 0000-9999 accepted. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| oneBasedDay | UTC observation-minus-start calendar days+1; can be zero or negative before the supplied start. | Required. Safe integer. |
| beforeCycleStart | Before Cycle Start | Required. Boolean. |
{
"input": {
"cycleStartDate": "2026-10-01",
"observationDate": "2026-10-05"
},
"output": {
"oneBasedDay": 5,
"beforeCycleStart": false
}
}Limitations and assumptions
- Dates before the supplied start can return zero or negative day indexes; no ovulation, fertility, pregnancy or cycle-normality prediction is made.
- 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.
Alternative or Complementary methods
Use verified records, validated instruments and qualified medical interpretation for actual screening, symptoms, fertility or other care decisions.
References
Similar or alternative tools
- Gynecology Item Recall Window Label
Label an item's caller-supplied recall window and source.
- Menstrual Diary Cycle Length One Pair Tool
Report one supplied onset interval with explicit date uncertainty.