basic

Ovulation Calculator

Estimate ovulation day and the fertile window.

Estimate the most likely ovulation day, the surrounding fertile window, and the next period start date from the last menstrual period and cycle length.

Priya Venkatesan By Priya Venkatesan
Reviewed by Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

days

Results

Enter values and click Calculate to see results.
Was this helpful?

How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Ovulation day = LMP + (cycle length − 14). The fertile window spans the 5 days before through 1 day after ovulation.

In depth

Estimate the most likely ovulation day, the surrounding fertile window, and the next period start date from the last menstrual period and cycle length.