Ovulation calculator
Enter the first day of your last period and your usual cycle length to see your fertile window, estimated ovulation day, next period and the due date if you conceive this cycle.
Fertile window
- Most fertile days
- Estimated ovulation
- Next period, and the earliest day for a pregnancy test
- Due date if you conceive this cycle
- Due date calculator
This cycle on the calendar
- Period starts
- Fertile window
- Most fertile
- Estimated ovulation
This calculator gives estimates for information only. It is not medical advice and not a method of contraception.
Your next six cycles
| Period starts | Fertile window | Ovulation | Due date if you conceive |
|---|
Ovulation by cycle length
| Cycle length (days) | Ovulation (days after your period starts) | Fertile window (days after your period starts) |
|---|---|---|
| 21 | 7 | 2–8 |
| 22 | 8 | 3–9 |
| 23 | 9 | 4–10 |
| 24 | 10 | 5–11 |
| 25 | 11 | 6–12 |
| 26 | 12 | 7–13 |
| 27 | 13 | 8–14 |
| 28 | 14 | 9–15 |
| 29 | 15 | 10–16 |
| 30 | 16 | 11–17 |
| 31 | 17 | 12–18 |
| 32 | 18 | 13–19 |
| 33 | 19 | 14–20 |
| 34 | 20 | 15–21 |
| 35 | 21 | 16–22 |
Count from the first day of your period. All values are estimates.
How to use it
- Enter the first day of your last period, the day bleeding started.
- Enter your usual cycle length: the number of days from the first day of one period to the first day of the next. If it varies, use the average of your last few cycles.
- Read your fertile window, the most fertile days and the estimated ovulation day, and see them on the calendar for this cycle and in the table for the next six.
How ovulation is estimated
Ovulation usually happens about 14 days before your next period starts. The time between ovulation and the next period is the most stable part of the cycle, so the calculator counts back 14 days from your expected next period. In a 28-day cycle that puts ovulation about 14 days after your period starts; in a 32-day cycle, about 18 days.
This is an average. The NHS notes that in most women ovulation happens around 10 to 16 days before the next period, so treat the date as an estimate and the whole fertile window as your best chance.
Your fertile window
According to the American College of Obstetricians and Gynecologists (ACOG), you can get pregnant from sex anywhere from 5 days before ovulation until 1 day after it. Sperm can survive in the body for about 3 days, sometimes up to 5, while the egg survives for about 24 hours.
The chance is highest in the last few days before ovulation and on the day itself. In a study of 221 women trying to conceive, published in the New England Journal of Medicine in 1995, the chance of conception per cycle rose from about 10% for sex five days before ovulation to about 33% on the day of ovulation.
If your cycle is irregular
If your cycle length changes a lot from month to month, a calendar estimate is less reliable. Ovulation test kits, which detect a hormone rise shortly before ovulation, can help narrow it down. According to the NHS, if you're 39 or under and have sex without contraception every 2 to 3 days, you're likely to get pregnant within a year; it suggests talking to a GP if you've been trying for a year or more.
Not a method of contraception
Don't use this calculator to avoid pregnancy. Ovulation can come earlier or later than expected, and sperm can survive for several days. ACOG notes that even with fertility awareness methods, which track daily body signs rather than dates alone, 12 to 24 out of 100 women become pregnant in the first year of typical use.
Frequently asked questions
When am I most fertile?
In the 5 days before ovulation and on ovulation day itself, with the best chance in the last two or three days. A chance remains until about a day after ovulation. The calculator shows these days for your cycle.
How is ovulation day calculated?
It is estimated as 14 days before your next expected period: the first day of your last period plus your cycle length, minus 14 days. In a 28-day cycle that is about 14 days after your period starts.
Can I get pregnant right after my period?
It's not very likely, but it is possible, especially with a short cycle. Sperm can survive for several days, so sex soon after your period can lead to pregnancy if you ovulate early.
When can I take a pregnancy test?
Most pregnancy tests can be used from the first day of a missed period. If you don't know when your period is due, the NHS suggests testing at least 21 days after you last had unprotected sex.
What if my cycle is irregular?
The estimate is less reliable when your cycle length varies. Use an average, consider ovulation tests, and talk to a doctor if your periods are very irregular or you have been trying for a year or more.
Can timing sex help choose a boy or a girl?
No. The 1995 New England Journal of Medicine study that mapped the fertile window found that, for practical purposes, the timing of sex in relation to ovulation has no influence on the baby's sex.
Sources
Also try: Pregnancy due date calculator