Women's Health Calculators
Free pregnancy due date calculator, ovulation calculator, and fertile window tracker. Plan your pregnancy and understand your menstrual cycle.
Women’s Health Calculators - Pregnancy & Fertility Planning
Planning a pregnancy or simply understanding your menstrual cycle requires accurate, reliable tools. These calculators are built on medically established methods - Naegele’s rule for due date estimation and the Luteal Phase Constant for ovulation prediction - and are designed to give you clear, actionable answers.
Pregnancy Due Date Calculator - Enter your last menstrual period, conception date, or ultrasound gestational age to calculate your Estimated Due Date (EDD). The calculator shows your current pregnancy week, trimester, and key milestone dates from first heartbeat detection to full-term status. Supports cycle length adjustment for more accurate dating when your cycle isn’t the standard 28 days.
Ovulation Calculator - Find your fertile window and peak ovulation day based on your LMP and average cycle length. Uses the Luteal Phase Constant (ovulation = cycle length − 14 days before next period) to calculate your 6-day fertile window. Projects the next 3 cycles so you can plan ahead.
How These Calculators Work
The Pregnancy Due Date Calculator uses three methods: (1) Naegele’s rule (LMP + 280 days, adjusted for cycle length), (2) conception date + 266 days, and (3) back-calculation from ultrasound gestational age. The most accurate EDD comes from an early ultrasound (8–12 weeks). The Ovulation Calculator uses the Luteal Phase Constant - most women ovulate 14 days before their next period, regardless of total cycle length. This is more accurate than the “day 14 of every cycle” misconception.
Frequently Asked Questions
How accurate are online pregnancy due date calculators?
LMP-based calculators are accurate within ±2 weeks for regular cycles. Early ultrasound (8–12 weeks) is more accurate (±5 days). Only ~5% of babies arrive on the exact due date - the EDD is a midpoint of a 5-week window (37–42 weeks).
Can I use the ovulation calculator for irregular cycles?
The ovulation calculator works best for cycles of 21–45 days. For irregular cycles, average your last 3 months and use that as input. For highly irregular cycles (varying by more than 7–9 days), ovulation predictor kits (OPKs) or basal body temperature tracking are more reliable than calendar calculations.
Is the fertile window the same as the ovulation day?
No. The fertile window spans 6 days: the 5 days before ovulation and the ovulation day itself. Sperm can survive 5 days in the reproductive tract, so intercourse before ovulation can result in pregnancy. The two peak days are the day before and the day of ovulation.
What is the medical disclaimer for these calculators?
These calculators are for informational and planning purposes only. They are not a substitute for medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider - an obstetrician, midwife, or gynecologist - for medical guidance on pregnancy, fertility, and reproductive health.