Home / Calculators / Cycle and ovulation / Ovulation and fertile window
Every calculator in one place, free and with no sign-up. Results show instantly — we don't hide them behind a form. Each one explains what the number means, where the reference ranges come from, and what it cannot tell you.
A calculator sees three or four figures. A specialist sees your history, your scans, your partner's results, and how you actually responded to treatment. If you're between cycles, changing clinics, or something in your results doesn't add up, a second opinion is the fastest way to find out whether anything would be done differently.
Free first consultation. No obligation to start treatment, and it doesn't affect your care at your current clinic.
These tools provide general information and are not a diagnosis or a substitute for assessment by a qualified clinician. Reference ranges and sources are stated on each calculator. Predictive estimates describe groups of people and cannot predict an individual outcome.
A calculator sees three or four figures. A specialist sees your history, your scans, your partner's results, and how you actually responded to treatment. If you're between cycles, changing clinics, or something in your results doesn't add up, a second opinion is the fastest way to find out whether anything would be done differently.
Free first consultation. No obligation to start treatment, and it doesn't affect your care at your current clinic.
Your fertile days with the chance of conception for each — they are not equal.
Date calculationExact arithmetic on the dating convention named below. Scan dating by your clinic takes precedence.
Ovulation is estimated by counting back from the next expected period, not forward from the last one. The luteal phase is the more stable half of the cycle, so counting back is more reliable when cycle length varies.
Source — Estimates only. Ovulation moves between cycles even in regular ones, and this calculation assumes a consistent luteal phase. An LH test, a mid-luteal progesterone, or follicle tracking measures what actually happened in a given cycle. It is not a contraceptive method.
The bands on this page are drawn from published sources but have not yet been reviewed by our medical team, and some vary by laboratory or assay. Check against the reference range printed on your own report.
First day of one period to the first day of the next
Leave at 14 unless a doctor has measured yours
Day 1 is the first day of full flow
That falls in the day 13-17 band.
Your result of 14 day of cycle sits in the highlighted band. Bands are reference points used alongside clinical findings — not a diagnosis.
The range most cycles fall into. Sperm survive up to about five days, so intercourse every one to two days across the window matters more than hitting one exact day.
Estimates only. Ovulation moves between cycles even in regular ones, and this calculation assumes a consistent luteal phase. An LH test, a mid-luteal progesterone, or follicle tracking measures what actually happened in a given cycle. It is not a contraceptive method.
Highlighted is the stage this measurement belongs to. It is a map of the process, not a schedule — timings vary by protocol and by clinic.
The luteal phase, from ovulation to the next period, is more consistent than the first half. If your cycle runs to 33 days, ovulation is nearer day 19 than day 14, and counting forward from your period would miss the window entirely.
Less so. If your cycle length varies by more than a few days, the window this produces is wide. Ovulation predictor kits or follicle tracking are more reliable, and irregular cycles are themselves worth investigating.
No. The test detects the LH surge, which normally triggers release. In luteinized unruptured follicle syndrome the surge happens and the egg is never released. Only ultrasound can tell the difference.
A calculator sees three or four figures. A specialist sees your history, your scans, your partner's results, and how you actually responded to treatment. If you're between cycles, changing clinics, or something in your results doesn't add up, a second opinion is the fastest way to find out whether anything would be done differently.
Free first consultation. No obligation to start treatment, and it doesn't affect your care at your current clinic.
Estimated from cycle length, not measured. An LH test or follicle tracking confirms what actually happened in a given cycle. Nothing here is a diagnosis or a substitute for assessment by a clinician.
A calculator gives you a number. These explain what it means, and what it does not.
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