# Ovulation Calculator

> Estimate ovulation dates and fertile windows for multiple cycles from the last period, average cycle length, and luteal phase.

Page: https://askcalculators.com/calculator/ovulation-calculator/
Definition: https://askcalculators.com/calculator/ovulation-calculator/definition.json
JSON Schema: https://askcalculators.com/calculator/ovulation-calculator/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/calculator/ovulation-calculator/?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 forecast; type=number; required; default=6; min=1; max=24

## Outputs
- nextOvulation: Estimated next ovulation; format=date; primary
- fertileWindow: Estimated fertile window; format=text
- nextPeriod: Estimated next period; format=date
- bestDays: Highest-probability days; format=text

## Formula
Estimated ovulation = next period start − luteal-phase length; fertile window = ovulation − 5 days through ovulation + 1 day.

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

Notice: Calendar estimates cannot confirm ovulation and are not reliable contraception by themselves.