🌸 Ovulation Calculator
Predict your most fertile days and next period from your cycle dates.
Quick answer: Ovulation usually happens about 14 days before your next period. If your last period started on October 1 and your cycle is 28 days, you will likely ovulate around October 15, with a fertile window of Oct 10 – Oct 16.
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Ovulation Calculator inputs
Result
Estimated ovulation
October 15, 2026
Fertile window: Oct 10 – Oct 16
- Most fertile days
- Oct 13 – Oct 15
- Next period expected
- October 29, 2026
An estimate only – not a method of contraception.
Your next cycles
| Period starts | Fertile window | Ovulation | Next period |
|---|---|---|---|
| Oct 1 | Oct 10 – Oct 16 | October 15, 2026 | Oct 29 |
| Oct 29 | Nov 7 – Nov 13 | November 12, 2026 | Nov 26 |
| Nov 26 | Dec 5 – Dec 11 | December 10, 2026 | Dec 24 |
| Dec 24 | Jan 2 – Jan 8 | January 7, 2027 | Jan 21 |
How ovulation is estimated
The luteal phase – the time from ovulation to the next period – is fairly constant at about 14 days for most people, while the phase before ovulation varies. So the calculator counts back from your next expected period.
Ovulation = first day of last period + cycle length − luteal phase (14 days)
Fertile window = ovulation − 5 days … ovulation + 1 day
Worked example
Your last period began on October 1 and your cycle is 28 days. Your next period is due October 29; counting back 14 days gives ovulation around October 15. The fertile window runs from October 10 to October 16, with October 13–15 the most fertile days.
Ovulation day by cycle length
| Cycle length | Ovulation (days after period starts) | Fertile window (days after) |
|---|---|---|
| 24 days | 10 | 5–11 |
| 28 days | 14 | 9–15 |
| 32 days | 18 | 13–19 |
| 35 days | 21 | 16–22 |
Signs that you are ovulating
- Clear, stretchy, “egg-white” cervical mucus.
- A small, sustained rise in basal body temperature after ovulation.
- A positive LH (ovulation predictor) test 24–36 hours beforehand.
- Mild one-sided pelvic twinges for some people.
These are estimates only: this calculator is not contraception and cannot confirm or rule out pregnancy.
Improving the prediction
Track at least three to six cycles and enter your average length – a single cycle can be misleading. If your cycles vary by more than seven to nine days, or you have not conceived after 12 months of trying (six months if you are over 35), talk to a doctor. Conditions such as polycystic ovary syndrome or thyroid problems can affect ovulation.
For general information only – not medical advice. Consult a healthcare professional.
Frequently asked questions
What is the fertile window?
It is the six days ending on the day after ovulation – the five days before ovulation plus ovulation day itself are the most important. Sperm can survive up to five days, while an egg lives 12–24 hours.
How accurate is an ovulation calculator?
It is a calendar estimate based on averages. Ovulation can shift by several days from cycle to cycle, especially with irregular periods, stress or illness. Ovulation tests or temperature tracking give more precise timing.
Can I use this to avoid pregnancy?
No. Calendar predictions are not reliable enough to be used as contraception. Speak to a healthcare professional about effective birth-control methods.
What if my cycles are irregular?
Use the average of your last several cycles, and treat the predictions as a rough guide. Ovulation predictor kits are much more useful when cycle length varies.