Ovulation Calculator
Find your fertile window and the best days to get pregnant. Enter your last period and cycle length for your ovulation day, next 3 fertile windows and estimated due date.
Average cycle is 28 days. Not sure? Count from the first day of one period to the first day of the next.
What this calculator shows you
Fertile window
The 6-day span when conception is possible.
Ovulation day
The estimated day your egg is released.
Best days
The 2–3 days with the highest chance of pregnancy.
Due date
Your estimated due date if you conceive this cycle.
Frequently asked questions
How does the ovulation calculator work?
Ovulation usually happens about 14 days before your next period. We take the first day of your last period, add your cycle length, and subtract 14 days to estimate your ovulation day — then build a fertile window around it.
What are the best days to get pregnant?
The highest chance of conceiving is in the 2 days before ovulation and on ovulation day itself. Because sperm survive up to 5 days, the full fertile window is the 5 days before ovulation through the day after.
How accurate is an ovulation calculator?
It’s a reliable estimate for regular cycles, but ovulation can shift with stress, illness or irregular cycles. For more precision, combine it with ovulation predictor kits (OPKs), basal body temperature tracking, or cervical mucus changes.
I have irregular periods — can I still use it?
You can, but the estimate will be less precise. Use your average cycle length over the last few months, and consider speaking to a gynaecologist — irregular cycles are common and very treatable.
Medically reviewed by First OPD Medical Team. Last reviewed on .
Based on average milestones from World Health Organization (WHO), ACOG, NHS UK. Educational only — not a substitute for personalised medical advice.
Trying to conceive? We’re with you
Book a fertility consult or gynaecologist on First OPD, and when you’re expecting, track every week with our free pregnancy tracker.