Enter your last period date and press Calculate to see your fertility predictions.
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Ovulation calculator — frequently asked
How does the ovulation calculator work?
It uses the calendar method: in a typical 28-day cycle, ovulation happens around day 14 (counting day 1 as the first day of your last period). The fertile window is the 5 days leading up to ovulation plus the day of ovulation itself — sperm can survive for 3-5 days, so intercourse during this window has the highest chance of conception. Enter your last period date and average cycle length, and the calculator computes your fertile window, ovulation day, and implantation date for the next 6 cycles.
When am I most fertile?
Your most fertile days are typically the 3 days before ovulation plus ovulation day itself. For a regular 28-day cycle, that's roughly days 11-15 (counting day 1 as your first day of menstruation). For longer or shorter cycles, the fertile window shifts proportionally — this calculator does the math for your specific cycle length.
Does this work for irregular periods or PCOS?
The calendar method is less reliable when cycles are irregular — which is common in PCOS, post-pregnancy, perimenopause, or under high stress. If your cycles vary by more than 7 days month-to-month, consider combining this calculator with ovulation predictor kits (LH strips), basal body temperature tracking, or cervical mucus monitoring for a more accurate fertile window.
What is the implantation date the calculator shows?
Implantation happens 6-12 days after ovulation, when a fertilised egg attaches to the uterine lining. The calculator estimates this window — useful if you're tracking for early pregnancy testing or noticing implantation symptoms (light spotting, mild cramping).
When can I take a pregnancy test?
Home pregnancy tests detect the hCG hormone produced after implantation. Most tests are accurate from 7-10 days after ovulation, with the most reliable results coming 14 days after ovulation (around the time your next period would start). The calculator shows the earliest test date for each cycle so you don't test too soon.
Is this calculator a substitute for medical advice?
No. It's an educational tool based on calendar averages. If you've been trying to conceive for over a year (or 6 months if you're over 35), or have known fertility concerns like PCOS, consult a gynaecologist or fertility specialist for personalised assessment.