How accurate is the period calculator?

Accuracy depends on how consistent your cycle is. The calculator mirrors Naegele-based projections, so regular cycles track closely while irregular cycles benefit from logging multiple months.

How do I calculate my ovulation date?

Ovulation is estimated by subtracting the luteal phase length from the projected start of your next period. Example: 28-day cycle with a 14-day luteal phase predicts ovulation on day 14.

What is the fertile window?

The fertile window covers the 5 days before ovulation, ovulation day, and the following day. Sperm can live up to 5 days, while the released egg survives about 24 hours.

How do I know which cycle phase I'm in?

The calculator tracks cycle days to display menstrual, follicular, ovulatory, or luteal phases and summarises typical symptoms for each stage.

What if my periods are irregular?

You can still enter your most recent data to get an estimate. For cycles that vary widely, use the predictions as a guide and continue logging start dates to refine the average length.

No. Calculations happen locally in your browser and reset when you refresh or close the page.

Can I use this for birth control?

This tool supports awareness of fertile and infertile days but is not a standalone contraceptive method. Discuss birth control options with a healthcare professional.

How far ahead can I predict my periods?

The tool lists up to 12 predicted cycles. Accuracy decreases the further you project, so review your data every few months.

Period & Ovulation Calculator

Enter your last period to see projected cycle dates, ovulation timing, and a seven-day fertile window

Next period

Jul 18, 2025

Estimated using your cycle length and luteal phase.

Fertile days

Jul 11 – Jul 17

Shows the six pre-ovulation days plus ovulation for conception planning.

Ovulation

Jul 15, 2025

Calculated by subtracting the luteal phase from the predicted next period.

Add your last period start date to unlock personalised predictions, cycle insights, and fertility tips.

🔒 100% Privacy Protected - No Data Storage

Your privacy is our priority. All calculations are performed locally in your browser. No personal data is stored, transmitted, or shared. Your cycle information disappears when you close the page, ensuring complete confidentiality.

Why Choose Our Period & Ovulation Calculator

Our advanced calculator provides accurate predictions and real-time insights to help you understand your reproductive health and plan for conception.

Cycle projection

Shows the next 12 predicted periods based on your inputs

Ovulation estimate

Applies luteal length to estimate ovulation and fertile window

Fertile window

Lists the 6 fertile days before ovulation plus the ovulation day

Phase insight

Highlights the phase you are currently in and expected symptoms

Privacy

Entries stay on-device; refresh to clear

Responsive

Optimised layout for phones, tablets, and desktops

Clinical references used

The calculator mirrors clinical rules of thumb used in obstetrics and reproductive endocrinology.

Cycle length assumptions

Predictions support cycles between 21 and 35 days, aligning with ACOG guidance on typical menstrual length ranges.

Ovulation timing

Ovulation is calculated by subtracting the luteal phase length (default 14 days) from the predicted next period, the same method clinicians use when estimating fertile windows.

Fertile window evidence

Conception probabilities peak in the 2 days before ovulation and remain elevated the day after, as summarised in WHO fertility awareness research.

Primary sources

Educational use only. Consult a qualified clinician about personalised medical questions.

Cycle phase quick reference

Use this table to understand common hormone trends and when to escalate symptoms to a clinician.

Menstrual (days 1-5)

Shedding of the uterine lining. Rest, hydration, and iron support are helpful.

Hormone focus:Estrogen & progesterone low; FSH begins to rise

Seek care if:Bleeding over 7 days, soaking pads hourly, or large clots

Follicular (days 6-13)

Estrogen rebuilds the uterine lining and energy often increases.

Hormone focus:Estrogen rising; FSH steady; LH low

Seek care if:Persistent spotting or pelvic pain

Ovulatory (day 14 ±2)

LH surge releases a mature egg. Fertile mucus may look like raw egg whites.

Hormone focus:LH surge; estrogen peaks; progesterone starts rising

Seek care if:Severe pain lasting over 48 hours or fever

Luteal (days 15-28)

Progesterone prepares the uterine lining. Track PMS symptoms for trends.

Hormone focus:Progesterone high; estrogen moderate; LH suppressed

Seek care if:Severe mood shifts, intense breast pain, or daily disruption

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Cross-check your cycle insights with these related calculators.

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