Women's Health Calculators
Free women's health calculators: period predictor, menstrual cycle tracker, due date, ovulation, BMI during pregnancy. Backed by IOM and medical guidelines.
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.
These calculators are for reference and educational planning purposes only, not a diagnosis or a substitute for care from an obstetrician, midwife, or gynecologist.
The Menstrual Cycle Calculator covers everyday cycle tracking and fertile-window awareness, independent of pregnancy status. The Pregnancy Due Date Calculator handles the most common pregnancy dating question, while the BMI During Pregnancy and Pregnancy Weight Gain Calculators work together to translate IOM 2009 guidelines into a personalised weight gain target once a pregnancy is confirmed - the BMI calculator establishes the starting category, and the weight gain calculator projects the expected cumulative gain by week from there.
Who Uses These Calculators
Anyone tracking their menstrual cycle for general awareness or family planning uses the menstrual cycle calculator to anticipate periods and fertile windows. People who are pregnant or have just found out use the due date calculator to estimate key dates before their first prenatal visit. Expecting parents and their care teams use the BMI and weight gain calculators as a personalized reference alongside - never instead of - the weight tracking done at prenatal appointments, since healthy gain ranges depend on factors (multiples, pre-existing conditions) that only a clinician can fully account for.
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.