About the Pregnancy & Due Date Calculator
Calculating your pregnancy progress and due date helps you stay informed and prepared for every milestone of your journey. Using clinical dating standards, our tool calculates gestational age and estimates key dates to align with your healthcare provider's timeline.
📅 Last Menstrual Period (LMP) Method
Commonly known as Naegele's Rule, this method calculates your due date by adding 280 days (40 weeks) to the first day of your last period. The formula assumes a standard 28-day menstrual cycle and is adjusted dynamically if your average cycle length is shorter or longer.
💕 Conception Date Method
If you know the exact date of conception (usually during ovulation), your due date is calculated by adding 266 days (38 weeks). Conception dating is highly accurate for tracked cycles or planned insemination.
🏥 Ultrasound Scan Method
Early ultrasound measurements (specifically CRL or Crown-Rump Length in the first trimester) are clinically considered the most reliable dating method. This calculator recalculates your gestational age and due date based on the scan date and weeks/days measured.
🧪 IVF Transfer Method
IVF due dates are calculated from the embryo transfer date. We add 263 days for a Day 5 blastocyst transfer, and 266 days for a Day 3 embryo transfer, matching standard reproductive medicine guidelines.
Gestational Age vs. Fetal (Fertilization) Age
It is common to confuse gestational age with actual fetal age. Gestational age measures the pregnancy starting from the first day of your LMP, which is roughly 2 weeks before conception actually occurs. Fetal age represents the actual age of the growing embryo from the date of conception. Therefore, when you are clinically '4 weeks pregnant', the fetus has a fetal age of about 2 weeks.
Pregnancy Weeks to Months Conversion Table
Pregnancy is calculated in weeks for clinical accuracy, but many people prefer to count in months. Because months vary in length and are not exactly four weeks long, this guide maps standard gestational weeks to calendar months and trimesters.
| Weeks | Month | Trimester |
|---|
| 1 – 4 | Month 1 | 1st Trimester |
| 5 – 8 | Month 2 | 1st Trimester |
| 9 – 13 | Month 3 | 1st Trimester |
| 14 – 17 | Month 4 | 2nd Trimester |
| 18 – 21 | Month 5 | 2nd Trimester |
| 22 – 26 | Month 6 | 2nd Trimester |
| 27 – 30 | Month 7 | 3rd Trimester |
| 31 – 35 | Month 8 | 3rd Trimester |
| 36 – 40 | Month 9 | 3rd Trimester |
Understanding the Trimesters of Pregnancy
A full-term pregnancy lasts approximately 40 weeks and is divided into three distinct phases called trimesters, each bringing unique developmental milestones.
- 1st Trimester: Weeks 1 to 12 — Rapid organogenesis, heartbeat initiation, and early ultrasound scans.
- 2nd Trimester: Weeks 13 to 27 — Fetal movement (quickening), gender reveal scan, and rapid growth phase.
- 3rd Trimester: Weeks 28 to 40+ — Final lung maturation, rapid weight gain, and preparation for labor.
How Accurate is Your Estimated Due Date (EDD)?
Only about 4% to 5% of babies are born exactly on their estimated due date. Most babies arrive within a two-week window before or after (between weeks 37 and 42). Delivery before 37 weeks is considered preterm, while delivery after 42 weeks is post-term. Your due date is a helpful guidepost, but baby development and delivery timing are unique to every pregnancy.
⚠️ Medical Disclaimer: The calculations and information provided by this tool are for educational and informational purposes only. They do not substitute for professional medical advice, diagnosis, or treatment. Always consult with your doctor or OB-GYN regarding your pregnancy progress and healthcare.