DeskTray

Ovulation Calculator

See your most fertile days and estimated ovulation date for the coming months. Nothing you enter leaves your device.

Runs in your browser. Nothing is uploaded Free, no sign-up Works on mobile
days
From the first day of one period to the day before the next. 28 is common; 21–35 is typical.
days
How many days you usually bleed.
days
Days from ovulation to your next period. Usually 14; change it only if you know yours (e.g. from ovulation tests).

Saved only in this browser’s storage; never sent anywhere. Untick to delete.

Estimates only. These dates assume a regular cycle and a 14-day luteal phase. Real cycles vary with stress, illness, travel, PCOS, thyroid problems, breastfeeding and hormonal medicines. Do not use this as contraception, and do not rely on it to plan or avoid pregnancy. For irregular, very painful or missed periods, see a gynaecologist.

How to calculate your ovulation date

  1. Pick the first day of your last period.
  2. Set your cycle length (and luteal phase if you know it).
  3. Read your fertile windows and add them to your calendar.

Features

  • Ovulation date and six-day fertile window
  • Most fertile days highlighted
  • Adjustable luteal phase
  • Estimated due date if you conceive
  • Calendar with colour and symbols, plus .ics export
  • Optional saving on this device only

Frequently asked questions

How is ovulation estimated?

Ovulation usually happens about 14 days before the next period, so it is estimated as the next period date minus your luteal phase (14 days by default). In a 28-day cycle that is day 15.

What is the fertile window?

The five days before ovulation and the day of ovulation. Sperm can live up to five days, while the egg lives about a day, so the two or three days up to ovulation are the most fertile.

How accurate is an ovulation calculator?

It is a rough guide. Ovulation can shift by several days from cycle to cycle. Ovulation test strips, basal body temperature or a follicle scan give a better picture.

Can I rely on the “safe days” to avoid pregnancy?

No. Calendar-based estimates are not reliable contraception. Speak to a doctor or gynaecologist about methods that work for you.

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