Ovulation Calculator
The fertile window lasts about 6 days each cycle — the 5 days before ovulation and ovulation day itself. This calculator estimates your ovulation date using your last menstrual period (LMP) and cycle length, then identifies the exact fertile window and peak fertility day for conception planning.
Frequently Asked Questions
How is ovulation date calculated?+
Ovulation typically occurs 14 days before your next period (the luteal phase is usually constant at 12–16 days). For a 28-day cycle: ovulation on day 14. For a 30-day cycle: ovulation on day 16. For a 35-day cycle: ovulation on day 21. This calculator adjusts based on your cycle and luteal phase length.
What is the fertile window?+
Sperm can survive inside the reproductive tract for up to 5 days. An egg is viable for 12–24 hours after ovulation. So the fertile window is approximately 6 days: 5 days before ovulation plus ovulation day itself. The 2–3 days before ovulation and ovulation day are the highest-fertility days.
What if my cycle is irregular?+
Irregular cycles make prediction harder. Track your cycle length for 3–6 months to find the average. You can also use OPK (Ovulation Predictor Kit) strips which detect the LH surge 24–36 hours before ovulation — more accurate than calendar prediction for irregular cycles.
Can I use this for contraception?+
This calculator is intended for conception planning, not contraception. Calendar-based methods have failure rates of 12–24% with typical use. For contraception, consult a healthcare provider about reliable methods. Ovulation timing can be affected by stress, illness, travel, and other factors.