When am I likely to ovulate?
The calculator places ovulation about 14 days before your next estimated period. Your actual timing may differ.
YOUR FERTILE WINDOW, AT A GLANCE
Ovulation Calculator
Estimate when you may ovulate and see your likely fertile window using your last period and usual cycle length.
Estimates, not certainties. Ovulation can vary even with regular cycles. This calculator cannot diagnose a condition or reliably prevent pregnancy.
Track your cycle and fertile days with Selin
Your web calculation gives you an estimate. Selin helps you track cycles over time, log symptoms, set reminders and see future predictions. These web dates are not transferred to the app.
- Log actual period starts
- Record your symptoms
- Set reminders
Quick answers about ovulation
What is my fertile window?
The days around ovulation when conception may be possible. Our displayed dates are planning estimates, not confirmed fertile days.
Can I ovulate earlier or later?
Yes, even with regular cycles. An average cannot anticipate every change.
Can a calculator tell the exact day?
No. Calendar arithmetic cannot confirm egg release.
How the Selin Ovulation Calculator works
Enter two details
Choose your last period’s first day and usual cycle length. No account is needed.
Explore ovulation and fertile days
Read your estimated ovulation date, timeline and three-cycle forecast.
Keep an ongoing record
Selin helps track cycles, symptoms and reminders. Web dates are not transferred.
How we calculate your dates
Estimated next period
Last period start + usual cycle length.
Estimated ovulation
Next estimated period − 14 days. This is an assumption, not evidence of ovulation.
Displayed fertile window
Estimated ovulation − 5 days through + 1 day. The extra day is a planning margin, not proof of fertility.
Why the dates can change
The interval from ovulation to a period varies. Repeating a fixed length cannot measure that variation.
NHS — Menstrual cycles and fertility
Estimates, not certainties. Ovulation can vary even with regular cycles. This calculator cannot diagnose a condition or reliably prevent pregnancy.
Understanding ovulation and fertility
What is ovulation?
Ovulation is the release of an egg from an ovary. A calendar can suggest timing but cannot establish whether release occurred.
How many fertile days are there?
ASRM describes a six-day biological window ending on ovulation day. This tool displays an additional day after the estimated date as a planning margin; it does not define your actual window.
Calendar estimate or hormone test?
This calculator measures neither LH nor progesterone, temperature or cervical mucus. An LH test detects a hormone rise; by itself, it does not prove egg release.
When should I try to conceive?
Regular sex every two to three days can avoid relying on a single predicted date. Choose an approach that suits you; a calendar cannot guarantee pregnancy.
What affects timing?
Stress, illness, hormonal changes and life stages may change your pattern. Irregular cycles make a single average less informative.
What about symptoms?
Clearer, stretchier cervical mucus may occur around ovulation. Symptoms alone cannot establish an exact ovulation date.
Can I use the dates for contraception?
No. Actual fertile days can fall outside the displayed range. Ask a healthcare professional about suitable contraception.
When should I seek advice?
Discuss persistently irregular or absent periods, new symptoms or concerns about conceiving with a healthcare professional. The calculator cannot diagnose fertility problems.
NHS — Periods and cycle patterns · Irregular periods and when to seek advice
Ovulation Calculator: Quick Facts
- What do I need?
- Last period start and usual cycle length.
- Is ovulation confirmed?
- No: this is calendar arithmetic.
- Can timing vary?
- Yes, including in regular cycles.
- What if cycles are irregular?
- Treat the dates as a rough illustration.
- Is this contraception?
- No. No day is labelled safe.
- Is it free?
- Yes, with no account required.
- Are my entries saved?
- No. Health entries stay in isolated browser memory and clear on reload.
Your questions, answered
Practical questions about ovulation, trying to conceive and your privacy.
Using the estimate
How do I calculate ovulation?
Enter the first day of your last period and your usual interval between period starts, then select Calculate ovulation.
What happens with a 28-day cycle?
The tool adds 28 days to the entered start and subtracts 14. For a 1 September start, that gives 15 September. It is not a universal cycle-day rule.
What if I do not know my cycle length?
Count the days between actual period starts over several cycles. The example value 28 is not personalized.
Understanding ovulation
Can ovulation occur soon after a period?
Yes, especially with earlier ovulation or shorter cycles. Bleeding dates do not establish safe days.
NHS — Menstrual cycles and fertilityCan ovulation happen late?
Yes. A later ovulation can shift the fertile window and the next period beyond a calendar estimate.
NHS — Menstrual cycles and fertilityHow accurate is this calculator?
There is no validated individual accuracy percentage. Future cycles may differ from the usual length you enter.
What if I use hormonal contraception?
This natural-cycle model may not apply. Withdrawal bleeding does not necessarily indicate an ovulatory cycle.
Limits and privacy
Can pregnancy occur outside the displayed window?
Yes. Actual ovulation may differ from the estimate, so unmarked dates are not a reliable boundary.
Can I use this as birth control?
No. This calculator is not a contraceptive method.
NHS — Fertility awareness and contraceptionDoes Selin store my dates?
No. These web entries remain in isolated browser memory. Store buttons and sharing links contain no health values.
Medically reviewed by
Elena VasilievaGynecologist and sexologist, Selin
Reviewed:
Sources and references
- NHS — Periods and cycle patterns
- NHS — Menstrual cycles and fertility
- NHS — Fertility awareness and contraception
- NHS — Irregular periods and when to seek advice
- NHS — Missed or late periods
- ASRM — How many fertile days are there?
- NHS — When should I try to conceive?
- ASRM — Calendar estimate or hormone test?
Your cycle doesn’t stop at one calculation.
Build your ongoing cycle history with Selin. Keep periods, symptoms and reminders together, at your own pace.
- Log actual period starts
- Record your symptoms
- Set reminders
