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Tools Pasal

Ovulation & Fertile Window Calculator

Find your fertile days and ovulation date from your last period — shown in English (AD) and Nepali (BS), with the next 3 cycles. Free and private.

First day of your last period
Average cycle length:days (default 28)

Enter your last period date to see your fertile window.

An estimate using the calendar method — ovulation can shift by 1–3 days, and it is not reliable for preventing pregnancy. For accuracy, combine with ovulation kits (OPK) or basal body temperature, and consult a doctor. Calculated in your browser; nothing is uploaded.

How to use it

Enter the first day of your last period (in AD or BS) and your average cycle length. The tool shows your fertile window, ovulation day, most fertile days and next period — plus a 3-cycle outlook to help plan ahead.

Understanding ovulation

  • Ovulation is when an egg is released — about 14 days before your next period.
  • The fertile window is the 5 days before ovulation plus ovulation day (sperm survive up to ~5 days).
  • Your most fertile days are the 2–3 just before ovulation.

Important notes

This is a planning estimate, most useful for those trying to conceive. It is not a contraceptive method — ovulation can shift, especially with irregular cycles. For accuracy, combine it with ovulation kits or basal body temperature, and see a doctor if you have concerns about fertility or your cycle.

Related: Period & Cycle Tracker, Pregnancy Due Date Calculator.

Frequently asked questions

How is the fertile window calculated?

Ovulation is estimated as your cycle length minus 14 days from the first day of your last period (the luteal phase is fairly constant at about 14 days). Your fertile window is the 5 days before ovulation plus ovulation day, because sperm can survive up to 5 days.

Which are my most fertile days?

The 2–3 days just before ovulation and ovulation day itself. Having intercourse during this window gives the best chance of conceiving.

Can I see the date in Nepali (BS)?

Yes — enter your last period date in English (AD) or Nepali (BS), and key dates are shown in both calendars.

Can I use this to avoid pregnancy?

No. The calendar method is not a reliable form of contraception — ovulation can move by several days, especially with irregular cycles. Use a proper contraceptive method and talk to a health professional.

How accurate is it?

It is an estimate. Stress, illness and hormonal changes can shift ovulation by 1–3 days. For accuracy, combine it with ovulation predictor kits (OPK), basal body temperature or cervical-mucus tracking.

Is my data private?

Yes. Everything is calculated in your browser; nothing is uploaded or stored.