Pregnancy Calculator – Due Date, Conception & Weeks Tracker

Pregnancy Calculator

First day of last menstrual period (LMP)

The Pregnancy Calculator (also known as a due date calculator or pregnancy due date calculator) estimates your baby’s due date, current pregnancy week, trimester, and remaining days. Whether you need a conception calculator to work backwards, a pregnancy week calculator to track weekly development, or a baby due date calculator for planning, this pregnancy tracker provides clear, step‑by‑step predictions based on your last period, conception date, or expected due date.

How Pregnancy Dates Are Calculated

1. Last Menstrual Period (LMP) method: Due date = LMP + 280 days (40 weeks).

2. Conception date method: Due date = conception date + 266 days (38 weeks).

3. Reverse method (due date known): LMP = due date – 280 days, conception = due date – 266 days.

4. Current week is calculated from LMP to today’s date.

Why Use a Pregnancy Calculator?

Plan ahead: Know your due date for medical appointments, maternity leave, and baby preparations.
Track development: Each week brings new fetal milestones – our pregnancy week calculator shows you where you are.
Understand trimesters: First (0‑12w), second (13‑27w), third (28‑40w) – each with different symptoms and developments.
Share with your provider: Provide accurate dates to your obstetrician.

This pregnancy due date calculator is based on standard medical formulas. For individualised care, always consult your healthcare provider. Bookmark this pregnancy tracker to use it throughout your pregnancy.

Understanding Pregnancy Trimesters

Pregnancy is divided into three trimesters. The first trimester (weeks 0‑12) is when the baby’s organs form. The second trimester (13‑27 weeks) is a period of rapid growth. The third trimester (28‑40 weeks) is when the baby gains weight and prepares for birth. Our pregnancy week calculator tells you exactly which week and trimester you are in.

Pregnancy Trimesters & Major Fetal Milestones Reference Table

Trimester	Gestational Weeks	Clinical Milestones & Scans	Fetal Biological Development
First Trimester	Weeks 1 – 12	Heartbeat detectable (W6), Nuchal Translucency scan (W11-13)	Organogenesis & embryo cell differentiation
Second Trimester	Weeks 13 – 27	Anatomy scan (W18-22), Quickening fetal movement (W18-20)	Rapid muscle, skeletal, & facial feature growth
Third Trimester	Weeks 28 – 40+	GBS screening (W35-37), Early term threshold (W37), Full term (W39)	Lungs mature & rapid brain adipose fat storage

Frequently Asked Questions About Pregnancy Dates

Can I use this if my cycle is irregular? Yes, but the estimate may be less accurate. Ultrasound dating is more precise.
How many weeks is a full‑term pregnancy? 40 weeks (about 9 months) from LMP, or 38 weeks from conception.
What if I already know my due date? Use the “Due date (reverse)” mode to calculate your LMP and conception date.
Is this a medical device? No, it is for informational purposes. Always confirm with your doctor.

How to Use This Pregnancy Tracker Throughout Your Journey

Save the result page or bookmark the link. As time passes, you can re‑calculate using the same LMP or due date to update your current week. This makes it a dynamic pregnancy tracker without needing to create an account.

Bookmark this pregnancy calculator to use it as your go‑to due date calculator, pregnancy due date calculator, conception calculator, and baby due date calculator. Share it with family and friends who are expecting.

Step‑by‑Step Manual Example

LMP: January 1, 2025 | Today: March 15, 2025

Due date = Jan 1 + 280 days = October 8, 2025

Days since LMP = 73 → weeks = 10 weeks + 3 days

Trimester = First (0‑12 weeks)

Weeks remaining = 40 – 10 = 30 weeks

Frequently Asked Questions about Pregnancy & Due Date

How is the estimated due date (EDD) calculated?

Naegele's Rule calculates EDD by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). If using conception date, add 266 days (38 weeks).

How accurate is an online pregnancy due date calculator?

Only about 5% of infants are delivered precisely on their estimated due date. Most births occur within a 2-week window (38 to 42 weeks). First-trimester ultrasound dating remains the gold standard for clinical precision.

What is the difference between gestational age and fetal age?

Gestational age measures pregnancy from the first day of your LMP (used by obstetricians). Fetal age measures actual developmental age from conception, which is approximately 2 weeks shorter.

How are pregnancy trimesters divided?

First Trimester: Weeks 1 to 12. Second Trimester: Weeks 13 to 27. Third Trimester: Weeks 28 to 40+.

How does IVF due date calculation work?

For IVF with a 3-day embryo transfer, add 263 days to transfer date. For a 5-day blastocyst transfer, add 261 days to transfer date.

Can my due date change during prenatal doctor visits?

Yes. If an early ultrasound (crown-rump length CRL) differs from your LMP due date by more than 5 to 7 days, your OB-GYN will adjust your official clinical due date.

What is considered a full-term pregnancy?

Early term: 37w 0d to 38w 6d. Full term: 39w 0d to 40w 6d. Late term: 41w 0d to 41w 6d. Post-term: 42w 0d and beyond.

What key fetal milestones occur in each trimester?

Week 6: Fetal heartbeat detectable by ultrasound. Week 12: Organogenesis complete. Week 20: Anatomy scan & gender identification. Week 24: Fetal viability threshold.