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When is your fertile window? An estimate based on your cycle.

Enter the first day of your last period and your average cycle length to see an approximate fertile window and ovulation date. This is an educational estimate — not a medical test.

Medically reviewed by Dr. Shweta Agarwal, MBBS, DGO · Last updated June 2026
Dr. Shweta Agarwal, Founder & Lead Fertility Specialist, at Aansh Hospital & IVF Center, Chandrapur Govt. ART-registered
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What is the fertile window?

The six days each cycle when conception is possible

Every menstrual cycle includes a window of roughly six days when sperm can survive long enough to fertilise a released egg. This window spans the five days before ovulation and the day of ovulation itself. Knowing approximately when this window falls can help couples planning a pregnancy focus their efforts — though calendar estimates are approximate and cannot replace clinical evaluation for those with concerns about fertility.

Ovulation typically occurs about 14 days before the end of your cycle (not 14 days after your period begins, unless your cycle is exactly 28 days). This calculator adjusts the estimate based on your actual cycle length.

Calculator

Estimate your fertile window

Enter the date your most recent period started.

Typical range: 21–35 days. If unsure, use 28.

For regular cycles

Why cycle length matters

Ovulation does not always happen on day 14. It occurs approximately 14 days before the end of your cycle. A 21-day cycle places ovulation around day 7; a 35-day cycle around day 21. This calculator adjusts for your actual cycle length.

For irregular cycles

When estimates are less reliable

Conditions such as PCOS, thyroid disorders, or significant stress can cause irregular cycles where ovulation timing varies. In these cases, calendar estimates are much less reliable. A follicular tracking ultrasound or ovulation induction treatment may be more appropriate — ask your doctor.

Related resources

Explore further

Medically reviewed by Dr. Shweta Agarwal, MBBS, DGO. Information on this page is educational and does not replace a medical consultation. Outcomes depend on individual clinical factors. This calculator provides an educational estimate only; it does not constitute medical advice, diagnosis, or treatment. Ovulation timing can only be confirmed clinically. Last updated June 2026.

Good to know

Frequently asked questions about the fertile window

What is the fertile window?
The fertile window is the span of days in a menstrual cycle during which pregnancy is biologically possible. It spans roughly five days before ovulation through to the day after ovulation — about six days in total — because sperm can survive in the reproductive tract for up to five days, while an egg is viable for only 12–24 hours after release. The days immediately before ovulation are typically considered the most favourable for conception.
How accurate is a fertile-window calculator?
A calendar-based calculator is a rough educational estimate, not a medical test. It works best for people with regular cycles of a consistent length. Factors such as stress, illness, significant weight change, or conditions like PCOS can shift ovulation unpredictably. For greater accuracy, methods such as basal body temperature (BBT) charting, ovulation predictor kits (OPKs) that detect the LH surge, or a follicular tracking ultrasound ordered by your doctor can pinpoint ovulation more reliably.
Can I get pregnant outside the fertile window?
Because ovulation can vary from cycle to cycle, it is possible — though less likely — for conception to occur outside the estimated window. Cycles that appear regular can still have natural variation of a few days. This is why calendar estimation alone is not a reliable method of contraception, and also why couples who are trying to conceive should not rely solely on calendar tracking if they have concerns about fertility.
When should I see a fertility specialist?
Clinical guidance recommends seeking an assessment with a fertility specialist if you are under 35 and have not conceived after 12 months of regular unprotected intercourse, or after 6 months if you are 35 or older. You should seek earlier evaluation if you have known risk factors such as irregular periods, a diagnosis of PCOS or endometriosis, a history of pelvic surgery, or if your partner has a known semen abnormality. Dr. Shweta Agarwal offers personalised fertility evaluations at Aansh Hospital & IVF Center.
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