Module · Pregnancy · Fertile Window

Ovulation Calculator

Find your fertile window and ovulation day from your last menstrual period. See a colour-coded cycle strip and estimated implantation window.

Your cycle

First day of last period

Average cycle length (days)

Luteal phase length (days, default 14)

Ovulation ≈ cycle length − luteal phase. This is a statistical estimate, not a medical diagnosis.

Your fertile window

Ovulation day

Sat, July 25, 2026

Fertile window

Jul 20 – Jul 25

Next period

Sun, August 9, 2026

Implantation window

Jul 31 – Aug 6

Cycle strip

Fertile

Ovulation

Next period

Guide

How Ovulation Calculator works

Step 01

Enter your last period

First day of your last menstrual period.

Step 02

Set cycle length

Average cycle length (default 28 days) and luteal phase (default 14).

Step 03

See the window

Ovulation day, 6-day fertile window, next period and estimated implantation window on a colour-coded strip.

FAQ

How does the calculator predict ovulation?+

Ovulation ≈ cycle length minus luteal phase (typically 14 days). This is a statistical estimate; ovulation tests give day-specific accuracy.

How long is the fertile window?+

About 6 days — the 5 days before ovulation plus ovulation day. Sperm can survive up to 5 days inside the female reproductive tract.

When is implantation?+

Typically 6–12 days after ovulation. This calculator shows that window so you know when a pregnancy test could turn positive.

More tools

Gestational age + trimester timeline from LMP.

Estimated delivery date from LMP or conception.

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