Ovulation Calculator: Fertile Window, Peak Days & 6-Month Cycle Calendar (PCOS Mode)

🗓️ Ovulation & Fertile Window Calculator

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First day of your last period (LMP)Day 1 = first day of full red flow.

Cycle type

Average cycle length (days)Normal adult range: 21–35 days.

Luteal phase length (days)Keep 14 if you don’t know it.

Calculator How it works Symptom checker Cycle chart & PCOS FAQ

How This Ovulation Calculator Works (ACOG & NHS Method)

Ovulation normally happens about 14 days before your next period — not on “day 14” for everyone. The second half of the cycle (the luteal phase) is fairly constant at 12–14 days, while the first half (the follicular phase) varies. That is why we subtract your luteal phase length from your cycle length:

Ovulation cycle day = Cycle length − Luteal phase length
Fertile window = 5 days before ovulation + ovulation day (sperm survive up to 5 days; the egg survives 12–24 hours).

The highest pregnancy chance is from intercourse during the 2 days before ovulation and on ovulation day (Wilcox et al., NEJM 1995). Couples with no fertility problems who have sex every 2–3 days do not need to time it exactly (NICE CG156).

Live Ovulation Symptom Checker — Am I Ovulating?

Tick the signs you notice today. The score weighs each sign by how reliably it predicts ovulation.

Positive LH / ovulation (OPK) test today or yesterday Clear, stretchy, slippery “egg-white” cervical mucus Cervix feels high, soft and open Mild one-sided lower abdominal pain (mittelschmerz) Increased sex drive Light spotting mid-cycle or breast tenderness Basal body temperature has risen 0.2–0.5 °C for 3 days

Cycle Length vs. Ovulation Day Chart (ACOG / NHS)

Assuming a 14-day luteal phase. Your personal result above uses your own luteal length.

Cycle length	Ovulation (cycle day)	Fertile window	Start LH tests	Implantation (approx.)
21 days	Day 7	Day 2 – Day 7	Day 5	Day 16 (≈9 DPO)
24 days	Day 10	Day 5 – Day 10	Day 7	Day 19 (≈9 DPO)
26 days	Day 12	Day 7 – Day 12	Day 9	Day 21 (≈9 DPO)
28 days	Day 14	Day 9 – Day 14	Day 11	Day 23 (≈9 DPO)
30 days	Day 16	Day 11 – Day 16	Day 13	Day 25 (≈9 DPO)
32 days	Day 18	Day 13 – Day 18	Day 15	Day 27 (≈9 DPO)
35 days	Day 21	Day 16 – Day 21	Day 18	Day 30 (≈9 DPO)
38 days	Day 24	Day 19 – Day 24	Day 21	Day 33 (≈9 DPO)
40 days	Day 26	Day 21 – Day 26	Day 23	Day 35 (≈9 DPO)
45 days	Day 31	Day 26 – Day 31	Day 28	Day 40 (≈9 DPO)

Tracking Ovulation With PCOS or Irregular Cycles

Use a range, not a single date. Enter your shortest and longest cycles — the calculator shows the full possible window.
LH strips can give false positives in PCOS because baseline LH is often high. Combine strips with cervical mucus and temperature charting.
Confirm ovulation with a mid-luteal (7 DPO) progesterone blood test or follicle-tracking ultrasound.
Cycles longer than 35 days or fewer than 8 periods a year suggest anovulation — letrozole is the first-line ovulation-induction medicine for PCOS (International PCOS Guideline 2023).
See a doctor after 12 months of trying (6 months if you are 35+), or sooner if periods are absent or very irregular.

Frequently Asked Questions

How accurate is an ovulation calculator?

For regular 21–35 day cycles a calendar estimate is usually within 1–3 days of true ovulation. Only about 30% of women ovulate exactly within the textbook window, so combine the calculator with LH tests, cervical mucus and temperature tracking for the best accuracy.

What is the 6-day fertile window?

It is the 5 days before ovulation plus ovulation day. Sperm can survive up to 5 days in fertile cervical mucus, while the egg lives only 12–24 hours, so sex before ovulation gives the highest chance of pregnancy.

Can I ovulate twice in one cycle?

You can release two eggs within the same 24-hour window (which can lead to fraternal twins), but you cannot ovulate again days later in the same cycle — rising progesterone after ovulation blocks another LH surge.

Does a positive LH test mean I ovulated?

A positive LH (OPK) test means ovulation is likely within the next 24–36 hours. It does not prove ovulation happened. A sustained temperature rise or a 7 DPO progesterone level above 3 ng/mL confirms it.

Can I use this calculator to avoid pregnancy?

No. Calendar methods alone have a typical-use failure rate of around 24% per year. This tool is for conception planning and education only and is not a contraceptive method.

When should I see a fertility specialist?

After 12 months of regular unprotected sex if you are under 35, after 6 months if you are 35–39, and right away if you are 40+, have irregular or absent periods, known PCOS, endometriosis, or a partner with a known sperm problem.

⚠️ Official Medical Disclaimer

This calculator is for informational and educational purposes only. It produces mathematical estimates based on published clinical literature (ACOG, ASRM, ESHRE, NICE, WHO, NEJM) and is not a medical diagnosis, treatment plan, or method of contraception.

Every body and every treatment cycle is different. Always discuss your results with a qualified OB-GYN, reproductive endocrinologist, or fertility specialist before making any medical decision. Seek urgent care for heavy bleeding, severe one-sided pain, fainting, or fever.

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