5 Tools

Women's Health Calculators

From conception to delivery and beyond — calculators for reproductive health, pregnancy tracking, fertility awareness, and obstetric assessment. Built on ACOG and WHO clinical standards. Completely private — no data ever leaves your browser.

ACOG & WHO guidelines Zero data stored Works on all devices PDF export
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Your privacy is protected. All calculations on this page run entirely within your browser. No dates, cycle data, or personal health information is transmitted to any server or stored anywhere. You can use these tools offline after first page load.
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🤰 Quick Due Date Estimate (Naegele's Rule) Full calculator with trimester timeline & milestones →
days
Select your last menstrual period date above to calculate your due date.

Pregnancy Trimester Guide

Key milestones by trimester. Our Due Date Calculator shows your personalised timeline with exact dates.

First Trimester
Weeks 1–12
Conception through organogenesis
  • Week 4: Positive pregnancy test
  • Week 6: Heartbeat detectable
  • Week 8: All major organs forming
  • Week 10: Embryo becomes fetus
  • Week 12: NT scan / first trimester screen
Second Trimester
Weeks 13–27
Growth & movement phase
  • Week 16: Anatomy scan scheduled
  • Week 18–20: Anomaly scan (20-week scan)
  • Week 20: Quickening (first movements)
  • Week 24: Viability threshold
  • Week 27: Glucose tolerance test
Third Trimester
Weeks 28–40+
Maturation & delivery preparation
  • Week 28: Third trimester begins
  • Week 32: Growth scan
  • Week 36: GBS swab, weekly checks
  • Week 37: Term (early term)
  • Week 40: Expected due date

Recommended Gestational Weight Gain (IOM 2009)

Based on pre-pregnancy BMI. Use our Gestational Weight Gain calculator to track progress week by week.

Underweight · BMI <18.5
28–40 lbs
12.5–18 kg total
0.5 kg/week in 2nd & 3rd trimester
Normal · BMI 18.5–24.9
25–35 lbs
11.5–16 kg total
0.4 kg/week in 2nd & 3rd trimester
Overweight · BMI 25–29.9
15–25 lbs
7–11.5 kg total
0.28 kg/week in 2nd & 3rd trimester
Obese · BMI ≥30
11–20 lbs
5–9 kg total
0.22 kg/week in 2nd & 3rd trimester
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Completely Private by Design
No account, no tracking, no server calls. Pregnancy dates and cycle data are among the most sensitive health information — we ensure it never leaves your device.
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Three Dating Methods
Our due date calculator accepts LMP, conception date, or ultrasound CRL — because not every pregnancy has a clear last period, and ultrasound dating is more accurate after 12 weeks.
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Cycle-Length Adjusted
Unlike most free tools that assume a 28-day cycle, our ovulation and due date calculators adjust for your actual cycle length — giving a more accurate result for cycles of 21–45 days.
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About Women's Health Calculators

Women's health encompasses a unique spectrum of clinical needs — from menstrual cycle awareness and fertility planning through pregnancy monitoring, obstetric assessment, and postpartum care. Our tools are designed to serve both patients seeking health information and clinicians needing quick reference calculations in obstetric, gynaecological, and midwifery practice.

Pregnancy Dating — Naegele's Rule and Ultrasound

The standard method for calculating estimated due date (EDD) is Naegele's Rule: add 280 days (40 weeks) to the first day of the last menstrual period (LMP). This assumes a regular 28-day cycle with ovulation on day 14. For cycles longer or shorter than 28 days, the EDD is adjusted: for a 35-day cycle, add 7 days; for a 21-day cycle, subtract 7 days.

ACOG recommends that when ultrasound dating differs from LMP dating by more than the gestational-age-specific threshold (±7 days before 9 weeks, ±7 days from 9–14 weeks, ±10 days from 14–16 weeks), the ultrasound date should take precedence. Our Due Date Calculator supports both LMP and ultrasound CRL-based dating with the appropriate correction factor.

Ovulation and the Fertile Window

Conception can only occur during the fertile window — approximately 6 days ending on the day of ovulation. Ovulation is not fixed at day 14 of the cycle; it occurs approximately 14 days before the next period. For a 28-day cycle this means day 14; for a 35-day cycle, day 21; for a 21-day cycle, day 7.

Sperm can survive in the female reproductive tract for up to 5 days, which is why the fertile window begins 5 days before ovulation. The egg itself is only viable for 12–24 hours after release. Our Ovulation Calculator determines the full fertile window based on your individual cycle length and displays conception probability by day as a visual chart — a feature not available on any comparable free tool.

Gestational Weight Gain — Why It Matters

Both excessive and insufficient weight gain during pregnancy carry clinical risks. Inadequate gain is associated with intrauterine growth restriction (IUGR), preterm birth, and low birthweight. Excessive gain is associated with gestational diabetes, pre-eclampsia, large-for-gestational-age (LGA) babies, caesarean delivery, and difficulty losing weight postpartum. The IOM (now National Academies) 2009 guidelines provide BMI-stratified targets that remain the standard of care in the US and most international guidelines.

Frequently Asked Questions

How accurate is the due date calculated from LMP? +
LMP-based dating is accurate to ±2 weeks in most cases when cycles are regular. Factors that reduce accuracy include irregular cycles, recent hormonal contraceptive use, and uncertainty about the LMP date. First-trimester ultrasound (7–12 weeks) is the most accurate method of pregnancy dating, with error of ±5–7 days. Only about 5% of babies are born on their predicted due date — the EDD is the midpoint of a normal delivery window of 38–42 weeks.
How do I calculate my fertile window? +
Ovulation typically occurs 14 days before your next expected period — not 14 days after your last period (unless your cycle is exactly 28 days). Your fertile window is the 5 days before ovulation plus the day of ovulation (6 days total). To find it: determine when your next period is due, subtract 14 days (ovulation day), then the window is 5 days before that through ovulation day. Use our Ovulation Calculator to determine your specific window based on your cycle length.
What is a normal menstrual cycle length? +
A normal menstrual cycle ranges from 21 to 35 days, with the average being 28 days. Periods lasting 2–7 days are considered normal. Cycles shorter than 21 days (polymenorrhoea) or longer than 35 days (oligomenorrhoea), highly variable cycle lengths (varying by more than 7–9 days between cycles), or absent periods (amenorrhoea) may warrant clinical evaluation. Our Menstrual Cycle Tracker flags cycles outside the normal range automatically.
What does an APGAR score of 7 at 1 minute mean? +
An APGAR score of 7–10 at 1 minute is considered normal and reassuring, indicating the neonate is in good condition. A score of 7 specifically usually reflects that one or two criteria (often colour and/or muscle tone) are not fully optimal — this is common and does not typically require intervention beyond routine care. The 5-minute APGAR is more prognostically significant; a score that remains below 7 at 5 minutes warrants closer monitoring and possible further assessment. Use our APGAR Score tool for documentation-ready records.
Is it safe to use online calculators for pregnancy planning? +
Online calculators like those on MediCalc Pro are excellent for providing general reference information, understanding your cycle, and preparing questions for your midwife or obstetrician. They are not a substitute for professional prenatal care. All pregnancies should be confirmed with a healthcare provider, and gestational age and due date should be formally confirmed at your booking appointment and first-trimester ultrasound. Our tools are designed to complement — not replace — clinical care.

Related Tools on MediCalc Pro

For neonatal assessment alongside APGAR, see the APGAR Score in Pediatrics. For pediatric growth assessment after birth, see Growth Chart Percentile. For BMI calculation before pregnancy, see the BMI Calculator. For vaccine schedule planning for mother and child, see Vaccine Schedule.

References & Guidelines

  • ACOG Practice Bulletin No. 700. "Methods for Estimating the Due Date." Obstet Gynecol. 2017;129(5):e150-e154.
  • Wilcox AJ, et al. "Timing of sexual intercourse in relation to ovulation." NEJM. 1995;333(23):1517-1521.
  • Institute of Medicine. Weight Gain During Pregnancy: Reexamining the Guidelines. National Academies Press, 2009.
  • Apgar V. "A proposal for a new method of evaluation of the newborn infant." Curr Res Anesth Analg. 1953;32(4):260-267.
  • World Health Organization. WHO Recommendations on Antenatal Care for a Positive Pregnancy Experience. WHO Press, 2016.
⚠️ Medical Disclaimer: Women's health calculators are for educational and informational purposes only. Pregnancy dating, fertility planning, and obstetric assessment must be confirmed by a qualified midwife, obstetrician, or healthcare provider. Do not make clinical decisions based solely on calculator output.
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