Cervical Mucus Fertile Window Calculator
Estimate your fertile window, peak fertility days, and an estimated ovulation day using your cycle length, optional luteal phase length, and cervical mucus observation.
Calculator
What is this calculator?
This tool estimates your fertile window by combining cycle timing with a daily fertility sign: cervical mucus. Cervical mucus is fluid made by the cervix, and it often changes across the menstrual cycle. When hormones rise before ovulation, mucus commonly becomes more noticeable, wetter, and sometimes stretchy. These changes help highlight when fertility may be higher compared with days that feel dry or sticky.
What you get from the results
- Estimated ovulation date based on cycle length and luteal phase length (if entered).
- Fertile window showing the days where conception may be more likely.
- Peak fertility days highlighting the most important timing near ovulation.
- Mucus interpretation to make daily tracking easier.
How it works
Your cycle begins on Day 1, the first day of bleeding. Ovulation is the release of an egg. The days after ovulation are called the luteal phase. Many people have a luteal phase around 14 days, but it can vary, which is why the luteal phase input is optional.
The calculation method used here
Estimated ovulation cycle day = cycle length − luteal phase length
The calculator converts that cycle day into a calendar date starting from your last period’s first day. To avoid common one-day shifts on different devices, dates are parsed and processed at local midnight.
Fertile window and peak days
- Fertile window: about 5 days before ovulation through ovulation day.
- Peak days: about 2 days before ovulation through ovulation day.
Cervical mucus guide
Track daily and record the most fertile sign you notice. If you see different types at different times, choose the type that seems most fertile.
Mucus types explained
Dry
Often a low-fertility sign that may appear early in the cycle or after ovulation.
Sticky
A transition sign that may appear as the body moves toward more fertile mucus.
Creamy
Often appears as fertility rises; commonly described as lotion-like.
Watery
A high-fertility sign that feels wet or very slippery.
Egg white
A peak fertility sign that is clear, slippery, and stretchy.
Benefits
1) Clear timing without guessing
You get a clear date range for fertile and peak days, making planning simpler than relying on averages alone.
2) Uses both timing and a body sign
Cycle length is an average. Mucus is a daily observation. Using both can help you notice earlier or later ovulation patterns.
3) Helps you track consistently
The calendar view makes it easy to visualize key days and keep a consistent routine across cycles.
Helpful reminder
Mucus can be influenced by hydration, illness, stress, semen, arousal fluid, lubricants, and some medications. If you have itching, burning, pain, strong odor, or unusual discharge, consider medical evaluation.