Ovulation Calculator
Enter the first day of your last period and your cycle length to see your estimated ovulation date, fertile window, next period and the next 6 cycles on a calendar.
Ovulation Calculator estimates when you ovulate and which days you are most fertile, from the first day of your last period, your average cycle length and your luteal phase. It shows your fertile window, next period, pregnancy test date and the next 6 cycles on a calendar, and exports them as an .ics file. Runs entirely in your browser — no upload, no signup. Made by FreeToolHub.
These dates are estimates. Ovulation can shift from cycle to cycle, so do not use them as birth control.
—
- Period
- Fertile window
- Ovulation
- Today
Your next 6 cycles
| Period starts | Fertile window | Ovulation |
|---|
How it works
The calculator adds your average cycle length to the first day of your last period to find your next period, then counts back your luteal phase (14 days by default) to estimate ovulation. Your fertile window is the five days before ovulation plus ovulation day, and the two days before ovulation plus ovulation day are your most fertile. It repeats this for the next 6 cycles, marks them on the calendar and lets you download them as an .ics file for your calendar app. Nothing you enter leaves your browser.
Frequently Asked Questions
How does the ovulation calculator work?
Ovulation usually happens about 14 days before your next period, not 14 days after the last one. The calculator adds your average cycle length to the first day of your last period to find your next period, then subtracts your luteal phase (14 days by default) to estimate ovulation. The fertile window is the five days before ovulation plus ovulation day itself.
What is the fertile window?
It is the six days in each cycle when sex can lead to pregnancy: the five days before ovulation and ovulation day. Sperm can survive up to five days in the body, while the egg lives for about 12 to 24 hours after release. The chance of pregnancy is highest on the two days before ovulation and on ovulation day.
What if my cycles are irregular?
Enter the average length of your last few cycles. If your cycle length changes by more than a few days from month to month, a calendar estimate is less reliable. Ovulation test strips, basal body temperature tracking or cervical mucus changes give a more precise picture of when you actually ovulate.
What is the luteal phase and should I change it?
The luteal phase is the time from ovulation to the start of your next period. It is fairly stable for each person, usually 12 to 14 days. Leave it at 14 unless you know your own luteal phase from ovulation tests or temperature tracking; then enter it for a more accurate estimate.
When can I take a pregnancy test?
Most home tests are reliable from the day your period is due, which is about 14 days after ovulation. Testing earlier can give a false negative because the pregnancy hormone hCG may not yet be high enough to detect.
Can I use this calculator as birth control?
No. Calendar estimates are not reliable contraception, because ovulation can shift from cycle to cycle. This tool is general information, not medical advice. If you have been trying to conceive for 12 months (or 6 months if you are over 35), talk to a doctor.