Pregnancy Calculator – Due Date, Weeks & Trimester Tracker
Our free pregnancy calculator helps you estimate your due date, find out how many weeks pregnant you are, and identify your current trimester — all based on your last menstrual period, conception date, or known due date. Simply enter one date and let the calculator do the rest. Whether you're newly pregnant or tracking your progress, this tool provides quick and accurate pregnancy timeline information.
Choose the date you know to calculate the rest.
Enter the date in YYYY-MM-DD format corresponding to your selected method.
Average number of days in your menstrual cycle (default is 28).
Your results will appear here
How to Use This Calculator
1. Select your calculation method: Last Menstrual Period (LMP), Conception Date, or Due Date — choose whichever date you know with certainty. 2. Enter the corresponding date in YYYY-MM-DD format in the 'Enter Date' field. 3. If your average cycle length differs from 28 days, adjust the 'Average Cycle Length' field accordingly for a more accurate result. 4. Click Calculate to instantly see your estimated due date, conception date, LMP date, weeks pregnant, current trimester, and days remaining until your due date. 5. Review the results — all key pregnancy milestones are displayed clearly. Consult your healthcare provider for medical confirmation.
How Is a Due Date Calculated?
The most widely used method for calculating a due date is Naegele's Rule, which adds 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). This assumes a standard 28-day cycle with ovulation occurring on day 14. If your cycle differs, the calculator adjusts accordingly.
Naegele's Rule Formula
Due Date = LMP + 280 days (adjusted for cycle length)
- For a 28-day cycle: Due Date = LMP + 280 days
- For a 30-day cycle: Due Date = LMP + 282 days
- For a 24-day cycle: Due Date = LMP + 276 days
Pregnancy Trimesters Explained
A full-term pregnancy is divided into three trimesters, each representing a distinct phase of fetal development:
- 1st Trimester (Weeks 1–12): Rapid cell division, organ formation, and early fetal development. Morning sickness and fatigue are common.
- 2nd Trimester (Weeks 13–26): The baby grows significantly, and most parents learn the baby's sex. Many find this the most comfortable trimester.
- 3rd Trimester (Weeks 27–40): The baby gains weight and prepares for birth. The mother may experience back pain, frequent urination, and Braxton Hicks contractions.
Conception Date vs. LMP
The LMP date is typically used because most people know when their last period began. Conception usually occurs about 14 days after the LMP (for a 28-day cycle), during ovulation. If you know your exact conception date, you can calculate backwards to find your LMP and forwards to your due date.
Why Only 38 Weeks from Conception?
Although pregnancy is counted as 40 weeks from LMP, fertilization only occurs around week 2. So actual fetal development is approximately 38 weeks from conception, but 40 weeks from LMP — both refer to the same due date.
Accuracy & Medical Confirmation
This calculator provides an estimate based on your input. An ultrasound performed between 8 and 20 weeks of pregnancy is the most accurate way to confirm your due date. Only about 5% of babies are born on their exact due date, so a range of plus or minus two weeks is considered normal.