Ovulation calculator
Your fertile window and ovulation day for the next six cycles.
From the first day of one period to the day before the next. 28 is typical.
Days from ovulation to your next period. Leave at 14 if you don’t know it.
Next ovulation (estimated)
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Enter the first day of your last period.
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How to calculate your fertile days
- 1
Enter the first day of your last period.
- 2
Enter your average cycle length.
- 3
Optional: enter your luteal phase if you track it.
- 4
See your fertile window, ovulation day and next periods.
When you’re most likely to conceive
Ovulation, when an egg is released, happens once per cycle, about 14 days before the next period starts. Sperm can survive up to five days, so the days before ovulation matter most. The calculator uses the first day of your last period and your cycle length to estimate your ovulation day and fertile window for the next six cycles.
An ovulation date and fertile days calculator: find your fertile window, plus a period calculator for your next periods.
How it’s worked out
- Ovulation day = first day of the period + cycle length − luteal phase (usually 14 days).
- Fertile window = the five days before ovulation, ovulation day and the day after.
- Next period = first day of the period + cycle length.
With a period starting on 1 October and a 28-day cycle, ovulation is around 15 October, the fertile window runs from 10 to 16 October, and the next period is due on 29 October. With a 32-day cycle, everything after the period moves 4 days later.
The luteal phase
The luteal phase is the time from ovulation to the next period. It’s fairly constant for each person, usually 12–14 days, while the first half of the cycle varies more. If you track ovulation with tests or temperature and know your luteal phase, enter it for a better estimate.
Know the limits
Cycles change with stress, illness, travel and age, and ovulation can come earlier or later than any calculation says. Ovulation tests, cervical mucus and basal body temperature give a better picture of a specific cycle. Don’t use these dates as birth control. If your cycles are very irregular, or you’ve been trying for a year (six months if you’re over 35), talk to a doctor.
Take a pregnancy test from the day your period is due; earlier tests often miss a pregnancy. If it’s positive, find your due date with the pregnancy due date calculator.
Frequently asked questions
When do I ovulate?
About 14 days before your next period starts. In a 28-day cycle that’s day 14; in a 32-day cycle, day 18. The calculator uses your cycle length to work it out.
What is the fertile window?
The six days ending on ovulation day, plus the day after. Sperm can survive up to five days, so the days before ovulation are the most likely to lead to pregnancy.
Can I use this as birth control?
No. Cycles vary from month to month, and ovulation can come earlier or later than predicted. Use it to understand your cycle, not to avoid pregnancy.
When should I take a pregnancy test?
From the day your period is due. Testing earlier often gives a false negative because the hormone level is still too low.