Cycle-based estimate
The calculator starts with your last period date and average cycle length to estimate the next cycle milestone.
Ovulation Calculator
Estimate ovulation day and fertile window from your last period and cycle length.
📅
Use the first full day of bleeding.
days
Typical cycle length from one period to
the next.
days
Default is 14 days if unsure.
days
Used to show estimated period
window.
Estimated cycle dates—
| Estimated ovulation date | — |
| Fertile window | — |
| Next period estimate | — |
| Possible test date | — |
Cycle length—
Luteal phase—
Estimated period end—
Fertile days6 days
Note: This is an estimate for education and planning. Cycle
irregularity, health conditions, medication, stress, and postpartum changes can affect ovulation timing.
How it works
Estimate your fertile window
This Ovulation Calculator estimates ovulation and fertile-window dates from the first day of your last period, average cycle length, and luteal phase.
It is intended for general planning only and cannot confirm ovulation, diagnose fertility issues, or replace medical advice.
Ovulation timing
Ovulation is estimated by subtracting the luteal phase from the next expected period date.
Fertile window
The fertile window is shown around the estimated ovulation date because sperm can survive for several days.
Not a diagnosis
Irregular cycles, conditions, and medications can change ovulation timing, so treat results as an estimate.
Frequently asked questions
It can be helpful when cycles are regular, but it is still only an estimate.
Ovulation can shift due to stress, illness, travel, sleep changes, medication, and hormonal variation.
The fertile window is the group of days when conception is more likely. It generally
includes several days before estimated ovulation and about one day after.
Yes. If your cycle length changes often, the estimate may be less reliable.
The luteal phase is the time between ovulation and the next period. Many calculators
use 14 days as a default.
No. This tool is for education and planning. Speak with a healthcare professional for
fertility questions or irregular periods.