# Estimate Ovulation Timing from a Period Date

> Estimate cycle-based ovulation and a possible conception window from a menstrual period date and stated cycle assumptions.

Page: https://askcalculators.com/health/conception/
Definition: https://askcalculators.com/health/conception/definition.json
JSON Schema: https://askcalculators.com/health/conception/schema.json
Version: 2.0.0
Maintained by: AskCalculators (software project; not a credentialed reviewer)
Qualified review: pending. Automated checks do not establish professional approval.
Page status: Live
Review status: Pending

## Use
Open the calculator page and enter values. Query-string parameters can restore and bookmark a calculation.
Example: https://askcalculators.com/health/conception/?lastPeriodDate=2026-08-01&cycleLength=28&lutealPhase=14&cycles=6

## Inputs
- lastPeriodDate: First day of last period; type=date; required; default=2026-08-01
- cycleLength: Average cycle length; type=number; required; default=28; min=20; max=45
- lutealPhase: Luteal phase length; type=number; required; default=14; min=8; max=20
- cycles: Cycles to plan; type=number; required; default=6; min=1; max=24

## Outputs
- fertileWindow: Next fertile window; format=text; primary
- bestDays: Highest-probability days; format=text
- ovulationDate: Estimated ovulation; format=date
- possibleDueDate: Possible due date; format=date

## Formula
Estimated ovulation = next period − luteal phase; conception window = ovulation − 5 through +1 days; possible due date = ovulation + 266 days.

## Rules
- Empty optional inputs are undefined, not zero.
- Hidden conditional inputs are ignored.
- Do not invent missing required inputs.

Notice: This planning estimate cannot confirm ovulation, conception, fertility, or pregnancy.