Fertile Window Calculator | Best Days to Get Pregnant

The fertile window is the group of days in a menstrual cycle when pregnancy is more likely. It usually includes the few days before ovulation and the day of ovulation. This calculator provides an estimate — results are approximate and may vary.

First day of last menstrual period

Average cycle length (days)

Most cycles are 28 days. Usual range is 21–45 days.

Your cycle length is outside the usual range for this calculator. Please consult a healthcare professional if your cycles are very irregular.

Trying to conceive?

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Your Fertile Window Estimate

Approximate — based on your cycle dates

Estimated ovulation date

Highest chance days

Next expected period

⚠️ This is an estimate, not a guarantee Cycle-based fertile window prediction is approximate. This tool must not be used as a contraception method. Irregular cycles reduce accuracy significantly.

What Is the Fertile Window?

The fertile window spans approximately 6 days — the 5 days before ovulation and the day of ovulation. This is because sperm can survive for up to about 5 days in the reproductive tract, while the egg survives for only about 12–24 hours after ovulation.

When Is the Best Time to Try to Conceive?

The highest chance of conception is generally the 1–2 days before ovulation and the day of ovulation. Regular intercourse every 1–2 days throughout the fertile window may maximise chances for couples trying to conceive.

Accuracy Limitations

This calculator assumes a regular cycle. Many factors can shift ovulation — including stress, illness, weight changes, breastfeeding, polycystic ovary syndrome (PCOS), thyroid conditions, and medications. Calendar-based estimates should not be relied upon as a contraceptive method.

When Should You See a Doctor?

Seek medical advice if you have been trying to conceive for 12 months (or 6 months if over 35), if your cycles are very irregular, if periods stop unexpectedly, or if you have severe pain or very heavy bleeding.

Related Fertility Tools

Frequently Asked Questions

It gives an estimate only. Ovulation can change from cycle to cycle, especially with irregular periods, illness, stress, breastfeeding, hormonal conditions, or age-related changes.

No. This calculator should not be used as a guaranteed method to avoid pregnancy.

The fertile window is the group of days when pregnancy is more likely. It usually includes the days before ovulation and the day of ovulation.

Seek medical advice if your cycles are very irregular, periods stop unexpectedly, bleeding is very heavy, you have severe pain, or you have difficulty conceiving after trying for a reasonable period.

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Educational Tool — Not Medical Advice

This calculator gives an estimate based on cycle dates. Ovulation can vary from cycle to cycle due to stress, illness, hormonal changes, irregular periods, breastfeeding, age, and medical conditions. This tool is not a diagnostic test and should not be used as a guaranteed method to achieve or avoid pregnancy.