How do I calculate my ovulation date?

Ovulation typically occurs 14 days before your next period (the luteal phase), regardless of cycle length. Subtract 14 from your cycle length to find the ovulation day. For a 28-day cycle: day 14. For a 35-day cycle: day 21. Enter your details above and the calculator does this automatically.

What is the fertile window?

The fertile window is the period each cycle when intercourse can result in pregnancy. It spans roughly 6 days: the 5 days before ovulation (when sperm can survive waiting for the egg) plus the day of ovulation itself. The egg only survives 12–24 hours after release, so timing matters significantly.

How do I use an ovulation calculator for irregular periods?

Irregular cycles make prediction harder. If your cycle varies between 28 and 35 days, use your shortest cycle to find your earliest possible ovulation (shortest minus 14) and your longest for the latest. This gives you a wider fertile window to track. Combine with OPK (ovulation predictor kit) tests for the most accurate results.

Can an ovulation calculator help choose the baby's sex?

The popular Shettles Method suggests that timing intercourse closer to ovulation may slightly favour a boy (Y sperm are faster but shorter-lived) while earlier in the fertile window may favour a girl (X sperm are slower but longer-lived). However, scientific evidence for this is weak — no natural method reliably determines sex, and each conception is roughly 50/50.

What is the luteal phase and why is it always 14 days?

The luteal phase is the period from ovulation to your next period. It's driven by the corpus luteum (the follicle that released the egg), which has a relatively fixed lifespan of about 14 days in most women. Unlike the follicular phase (before ovulation), which varies with cycle length, the luteal phase is typically constant at 12–14 days. Luteal phase defect (less than 10 days) can sometimes affect fertility.

What are the signs of ovulation?

Physical signs include: light mid-cycle spotting, a slight rise in basal body temperature (BBT) after ovulation (0.2–0.5°C), changes in cervical mucus (becoming clear and stretchy like raw egg white around ovulation), mild one-sided pelvic pain (mittelschmerz), and a positive LH surge on an OPK test. BBT charting and OPK tests together are the most reliable tracking methods.

How soon after my period can I get pregnant?

It depends on your cycle length. For short cycles (21–24 days), ovulation can occur as early as day 7–10, meaning fertile days begin just after a period ends. For longer cycles (35+ days), fertile days are later. Sperm can survive up to 5 days, so unprotected sex near the end of a period can still result in pregnancy for women with short cycles.

What if my cycle is longer than 35 days?

Cycles over 35 days are considered irregular or oligomenorrhea. Long cycles can be associated with PCOS (polycystic ovary syndrome) or thyroid conditions. Ovulation still occurs before your period — it just happens later in the cycle. If your cycles are regularly over 35 days or are highly variable, consult a healthcare provider or gynaecologist.

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Ovulation Calculator

Day of Last Period

Month of Last Period

Year of Last Period

yyyy

Average Cycle Length

days

About this tool

Find your fertile window and ovulation date

The Ovulation Calculator predicts when you are most likely to ovulate and identifies your fertile window — the days each cycle when pregnancy is possible. Based on your last period date and cycle length, it calculates your ovulation date and maps out the next three cycles.

Ovulation typically occurs 14 days before your next period (the luteal phase length), regardless of cycle length. This means:

28-day cycle → ovulation at day 14
35-day cycle → ovulation at day 21
24-day cycle → ovulation at day 10

The fertile window spans 5 days before ovulation plus ovulation day itself — because sperm can survive in the reproductive tract for up to 5 days, while the released egg lives only 12–24 hours.

Note: This calculator provides estimates based on average cycle timing. Ovulation can shift due to stress, illness, travel, and hormonal changes. For confirmed ovulation detection, use LH ovulation test strips (OPK tests) alongside this calculator.

Example

Last period: 1 June 2025. Cycle length: 32 days.

Ovulation = day 32 − 14 = day 18 → 18 June 2025.

Fertile window: 13 June – 19 June 2025 (5 days before + ovulation day + 1 day).

Next period expected: 3 July 2025 (1 June + 32 days).