Ovulation Calculator
Find your ovulation date and fertile window to help plan conception or understand your menstrual cycle.
Last Menstrual Period
days
Ovulation Date
15 January 2026
Fertile Window Start
10 January 2026
Fertile Window End
16 January 2026
Next Period Expected
29 January 2026
How to Use This Calculator
Enter the first day of your last menstrual period and your average cycle length (typically 28 days but ranges from 21–40 days). The calculator determines your estimated ovulation day and shows the fertile window — the days when pregnancy is most likely if intercourse occurs.
The Formula
Ovulation Day = LMP + (Cycle Length − 14)
Fertile Window = Ovulation Day − 5 to Ovulation Day + 1
(Sperm survives up to 5 days; egg survives 12–24 hours)
Next Period = LMP + Cycle Length
Example (28-day cycle, LMP Jan 1):
Ovulation = Jan 1 + 14 = January 15
Fertile Window = January 10–16
Next Period = January 29
FAQ
Calendar-based ovulation prediction is a useful guide but is not highly reliable for contraception — irregular cycles, stress, illness, and travel can shift ovulation timing significantly. For family planning purposes, this should be combined with basal body temperature tracking, ovulation predictor kits (LH strips), or cervical mucus observation. For contraception, use medically approved methods.
Yes, but with lower accuracy. Use your average cycle length over the past 3–6 months. If cycles vary by more than 7 days (e.g. 24–35 days), your fertile window is wider and harder to predict. Women with PCOS often have very irregular cycles — in this case, tracking LH surges with ovulation test strips gives more reliable results.
The highest pregnancy probability is the day before and day of ovulation. Having intercourse every 1–2 days during the 5-day fertile window maximises chances. Sperm can survive up to 5 days in fertile cervical mucus, so starting a few days before ovulation is effective. Most Nigerian gynaecologists recommend trying for 12 months before investigating for infertility (6 months if over 35).