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When your cycle length changes month to month, calendar-based ovulation prediction is only a starting point. Enter your shortest and most recent cycle to see an estimated fertile window — but for irregular cycles the most reliable approach is to confirm ovulation with LH (ovulation predictor) kits, basal body temperature, or cervical-mucus tracking. This page explains how to combine the calculator with those methods.
Enter your last period date and press Calculate to see your fertility predictions.
Eight more calculators families use alongside this — all free, no account needed.
You can, but treat the result as an estimate. Calendar prediction assumes a fairly consistent cycle. If your cycles vary by more than about 7–9 days, widen your fertile window and confirm ovulation with LH strips or basal body temperature for accuracy.
Combine methods: LH ovulation predictor kits detect the hormone surge 24–36 hours before ovulation; basal body temperature rises after ovulation; and cervical mucus becomes clear and stretchy near your fertile peak. Using two together is far more reliable than the calendar alone when cycles vary.
See a gynaecologist if your cycles are consistently shorter than 21 days or longer than 35 days, you skip periods for three months or more, or you've been trying to conceive for over a year (6 months if over 35). Irregular cycles can point to PCOS, thyroid problems, or other treatable causes.
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.
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.
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).
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 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.
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.