Ovulation Calculator (Free Fertility Calculator)
Use this free ovulation calculator to find your estimated ovulation date and fertile window. Enter the first day of your last period and your average cycle length to see when you’re most likely to conceive, your next period date, and your next 3 ovulation dates.
Ovulation Calculator
📅 Your Cycle at a Glance
How to Use the Ovulation Calculator
Enter the first day of your last period, your average cycle length, and your luteal phase length. If you’re unsure of your luteal phase, leave it at the default 14 days which is the average. Click Calculate for your full fertility forecast.
What Is Ovulation?
Ovulation is when your ovary releases an egg. It typically happens around the middle of your menstrual cycle — about 14 days before your next period. The egg survives for 12-24 hours after release, but sperm can survive for up to 5 days, which is why the fertile window spans several days around ovulation.
How Is Ovulation Calculated?
Ovulation is estimated using the formula: Ovulation Day = Cycle Length − Luteal Phase Length. For a standard 28-day cycle with a 14-day luteal phase, ovulation occurs around day 14. For longer or shorter cycles the date shifts accordingly.
What Is the Fertile Window?
The fertile window is the period when pregnancy is possible. It spans the 5 days before ovulation and the day after — a total of 7 days. The days immediately before and on the day of ovulation are when conception is most likely.
FAQs
How accurate is this ovulation calculator?
This calculator provides estimates based on your average cycle length. Actual ovulation can vary by several days depending on stress, illness, or hormonal changes. For precise tracking consider using ovulation predictor kits alongside this tool.
What is the luteal phase?
The luteal phase is the second half of your cycle — from ovulation until your next period. It typically lasts 10-17 days, with 14 days being the average.
Can I get pregnant outside the fertile window?
It’s very unlikely but not impossible due to cycle variations. The fertile window shown is based on your average cycle and may shift if your cycle length changes.
How long does ovulation last?
The egg is only viable for 12-24 hours after release. However sperm can survive inside the body for up to 5 days, which extends the effective fertile window significantly.
What if my cycle is irregular?
This calculator works best with regular cycles. If your cycle varies significantly each month, tracking methods like basal body temperature or ovulation predictor kits may give more accurate results.
Is this calculator free?
Yes, completely free with no sign-up required.