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Ovulation and Fertile Window Estimate — result sheet
Estimate a next period, ovulation date, and fertile window from cycle assumptions.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Next period = last period + cycle length; estimated ovulation = next period - luteal phase; fertile window = five days before through one day after ovulation.
The assumptions are explicit because calendar predictions cannot observe actual ovulation or account for irregular cycles.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- First day of last period
- Average cycle length — days; minimum 21; maximum 45
- Estimated luteal phase — days; minimum 10; maximum 16
Worked example
| Input | Value |
|---|---|
| First day of last period | 2026-01-01 |
| Average cycle length | 28 |
| Estimated luteal phase | 14 |
Estimated ovulation is 2026-01-15 and the next period is 2026-01-29.
Assumptions and limits
- The cycle is regular enough for a calendar estimate.
- The fertile window is not contraception or an infertility diagnosis.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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