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Ovulation Calculator.

Find your fertile window and the day you are most likely to ovulate.

Ovulation Calculator | TrueScan®️

Calculate your fertile window

Add your average cycle length and the first day of your last period.

28 days
21 45
Typical range: 21 to 45 days. Average is 28.
If your period started today, use today's date.
Your Result
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Ovulation Day
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Fertile Window
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Next Period
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Next Fertile Window
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Your cycle at a glance

A visual map from your last period to your next period.

Period Fertile window Ovulation day Other days
This is not medical advice. The calculator gives an estimate based on a standard 14-day luteal phase model. Every cycle is different. Please consult your doctor for guidance specific to your health.

Understanding your fertile window

Your menstrual cycle has two main phases. The follicular phase runs from the first day of your period until ovulation — estrogen rises and an egg matures in the ovary. The luteal phase runs from ovulation to the start of your next period — progesterone prepares the uterus for a possible pregnancy.

 

For most cycles the luteal phase is around 14 days long. That is why ovulation is estimated by counting back 14 days from your expected next period. The fertile window is the five days before ovulation plus the day of ovulation itself, since sperm can survive for up to five days.

 

If your cycles are irregular, this calculator can still give a rough estimate. Combine it with other signs of ovulation for better accuracy.

Key signs of ovulation

  • Clear, stretchy cervical mucus (similar to raw egg whites)
  • A small rise in basal body temperature
  • Mild pelvic or one-sided abdominal pain
  • Breast tenderness
  • Increased libido
  • A positive result on an LH ovulation test

Common questions

Short, clear answers to what most people ask.

What is an ovulation calculator?

It is a tool that estimates the day you are most likely to ovulate and your fertile window, based on your cycle length and the first day of your last period.

How accurate is it?

It is reliable for women with regular cycles. For irregular cycles, the estimate is rougher — combine it with other signs of ovulation or a TrueScan® LH Ovulation Test for better accuracy.

When is the best time to try for a baby?

Your highest chance of conception is during the fertile window — the five days before ovulation and the day of ovulation itself. The day before and the day of ovulation are usually the most likely days to conceive.

Can I use this if my periods are irregular?

Yes, but the estimate will be less precise. Track your last three cycles, take an average, and use that as your cycle length. Add an LH ovulation test for a stronger signal.

Is this calculator a method of birth control?

No. It should not be used to prevent pregnancy. Please speak to your doctor about reliable contraception options.

Is my data saved anywhere?

No. The calculator runs entirely in your browser. Your last period date and cycle length never leave your device.

When should I see a doctor about fertility?

If you are under 35 and have been trying to conceive for over a year, or over 35 and trying for more than six months, it is a good time to consult a gynaecologist.
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