Ovulation Calculator
Enter your last period and cycle length to see your fertile window, ovulation day, and best days to conceive.
Your cycle
Next 6 cycles
| Cycle | Fertile window | Ovulation | Period due |
|---|
Your fertile window
-
Enter your last period date to begin
Ovulation day
-
Best 3 days
-
Highest chance
Next period
-
If you conceive
-
Estimated due date
Your cycle at a glance
| Phase | Dates | Cycle days | Length | What happens |
|---|
Not a contraceptive method. Ovulation shifts between cycles, so calendar timing is unreliable for avoiding pregnancy. Use a proven contraceptive instead.
Trying for over a year - or six months if you are over 35 - or cycles very irregular? See a gynaecologist.
Frequently asked questions
When am I most likely to get pregnant?
The fertile window is roughly the five days before ovulation plus the day of ovulation. Chances peak in the two to three days immediately before ovulation - sperm survive several days in the reproductive tract, while the egg lives only about 12 to 24 hours after release.
How is the ovulation date calculated?
By counting the luteal phase backwards from your expected next period. The luteal phase (ovulation to period) is the more consistent half of the cycle, typically 12-16 days. For a 28-day cycle with a 14-day luteal phase, ovulation lands around day 14.
Can my fertile window overlap my period?
Yes, and on a short cycle it often does. The fertile window is fixed relative to ovulation, not to bleeding - so if you have a short cycle, a long period, or both, ovulation follows soon enough after your period that the window reaches back into the bleeding days. Because sperm survive up to five days, sex during your period can result in pregnancy. This is why the wheel above draws bleeding and the fertile window as two separate rings rather than one: they are different things about the same day, and neither cancels the other. "You cannot get pregnant on your period" is false.
Is the menstrual phase separate from the follicular phase?
Not really - menstruation happens during the early follicular phase. The follicular phase runs from day 1, the first day of bleeding, until ovulation. Most cycle charts show "menstrual" as its own slice because bleeding is the part you can actually observe, and this one does too, but the underlying hormonal phase continues straight through it.
Is an ovulation calculator accurate?
It is an estimate from averages, not a measurement. Real ovulation varies cycle to cycle. For a sharper signal, combine it with ovulation predictor kits, basal body temperature charting, or cervical mucus observation.
Can I use this to avoid pregnancy?
No. Calendar-based prediction is not reliable contraception - ovulation can shift by several days with illness, stress or travel. Use a proven contraceptive method.
What if my cycles are irregular?
If your cycle length varies by more than a few days, calendar prediction loses accuracy. Track three to six cycles to find your range and use the shortest and longest to bracket a wider fertile window. Persistent irregularity is worth raising with a gynaecologist - conditions like PCOS and thyroid disorders are common and treatable.