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Understand your estimate
Due Date Calculator
Calculate your pregnancy due date, current pregnancy week, trimester, conception date, and important milestones instantly.
More Health Calculators
How the Due Date Calculator Works
1
Enter Last Period Date
Select the first day of your last menstrual period.
2
Choose Cycle Length
Enter your average menstrual cycle length.
3
Calculate Due Date
Click Calculate to estimate your pregnancy due date.
4
View Pregnancy Details
See due date, trimester, pregnancy week, and milestones.
Due Date Formula
Due Date = Last Menstrual Period + 280 Days
Pregnancy due dates are commonly estimated using Naegele's Rule, which adds 280 days (40 weeks) to the first day of the last menstrual period.
Example Calculation
Input: LMP: 1 January 2026
Output: Estimated Due Date: 8 October 2026
Common Uses
- • Pregnancy Planning
- • Prenatal Care
- • Tracking Pregnancy Progress
- • Doctor Appointments
- • Baby Arrival Preparation
Questions about this calculator
A Due Date Calculator provides an estimate based on your last menstrual period. Actual delivery dates may vary.
Naegele's Rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period.
Yes, but the estimate may be less accurate. Consult your healthcare provider for a more precise estimate.
The calculator determines whether you are in the first, second, or third trimester based on your pregnancy week.
First-trimester dating ultrasounds measure crown-rump length, which provides an accurate assessment of fetal development. If ultrasound measurements differ significantly from your LMP estimate, your healthcare provider may update your official estimated due date.
What Is a Due Date Calculator?
A Due Date Calculator helps estimate the expected delivery date of a baby based on the first day of the last menstrual period (LMP). Most pregnancies last around 40 weeks (280 days), making it possible to predict an estimated due date and track pregnancy progress.
How Pregnancy Due Dates Are Calculated
Healthcare professionals commonly use Naegele's Rule to estimate a due date. The calculation assumes a standard 28-day menstrual cycle and adds 280 days to the first day of the last menstrual period.
| Calculation Method | Formula |
|---|---|
| Naegele's Rule | Last Menstrual Period + 280 Days |
| Pregnancy Duration | 40 Weeks |
Pregnancy Trimesters Explained
Pregnancy is divided into three trimesters, each representing a different stage of fetal development.
| Trimester | Weeks | Description |
|---|---|---|
| First Trimester | 1 - 12 Weeks | Early development of organs and body systems. |
| Second Trimester | 13 - 27 Weeks | Rapid growth and noticeable pregnancy changes. |
| Third Trimester | 28 - 40 Weeks | Final growth and preparation for birth. |
Important Pregnancy Milestones
| Week | Milestone |
|---|---|
| 4 | Pregnancy test may become positive |
| 8 | Baby's major organs begin forming |
| 12 | First trimester completed |
| 20 | Mid-pregnancy anatomy scan |
| 28 | Third trimester begins |
| 37 | Pregnancy considered full term |
| 40 | Estimated due date |
Factors That Can Affect a Due Date
- Irregular Menstrual Cycles: May change ovulation timing.
- Cycle Length: Longer or shorter cycles can affect calculations.
- Ultrasound Measurements: Can provide a more accurate estimate.
- Multiple Pregnancies: Twins and triplets often arrive earlier.
- Medical Conditions: Some conditions may impact pregnancy duration.
Estimated Due Date vs Actual Delivery Date
Only a small percentage of babies are born exactly on their estimated due date. Most deliveries occur within a few weeks before or after the predicted date. The due date should be viewed as a guideline rather than a guarantee.
| Delivery Timing | Classification |
|---|---|
| Before 37 Weeks | Preterm |
| 37 - 38 Weeks | Early Term |
| 39 - 40 Weeks | Full Term |
| 41 Weeks+ | Late Term |
Preparing for Your Baby's Arrival
- Attend regular prenatal appointments.
- Maintain a healthy and balanced diet.
- Take prenatal vitamins as recommended.
- Stay physically active if approved by your doctor.
- Prepare essential baby supplies before the due date.
Why Use an Online Due Date Calculator?
A Due Date Calculator provides a quick and convenient way to estimate your baby's arrival date, track pregnancy progress, determine your trimester, and plan important milestones throughout your pregnancy journey.
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Reviewed by the DevCalc Editorial Team
This page is maintained through a documented review of formula selection, units, limitations and clear medical disclaimers. DevCalc is founded and maintained by software engineer Aditya Singh. Important financial, health, legal and government figures should still be confirmed with the relevant official source.
This calculator is for general informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Consult a qualified healthcare provider for health decisions.