Pregnancy Due Date Calculator
Find your baby's estimated due date, gestational age, and trimester timeline instantly — based on your last period or conception date.
Enter Your Dates
The first day your last period started.
Adjust if your cycle is consistently shorter or longer than 28 days.
This calculator provides an estimate only. Your healthcare provider will confirm your due date with an ultrasound. Only ~5% of babies arrive on their exact due date.
Enter your date above
Your due date, gestational age, and trimester timeline will appear here.
On This Page
What Is a Pregnancy Due Date?
A pregnancy due date (also called the estimated date of delivery, or EDD) is the calendar date when your baby is most likely to be born. It is calculated as 40 weeks (280 days) from the first day of your last menstrual period — a method known as Naegele's Rule, developed by German obstetrician Franz Karl Naegele in the 19th century and still used by OB/GYNs worldwide today.
It's important to understand that a due date is an estimate, not a precise prediction. Only about 5% of babies are born on their exact due date. Most births occur within the "term" window — between 37 and 42 weeks of pregnancy. Your healthcare provider will use ultrasound measurements, especially in the first trimester, to confirm or adjust your due date.
This calculator gives you your EDD along with your current gestational age (how far along you are), a countdown to your due date, and the end dates for each trimester.
How to Calculate Your Due Date
There are two primary methods for calculating a due date:
Method 1: Last Menstrual Period (LMP)
Formula: Due Date = LMP + 280 days + (Cycle Length − 28 days)
The standard 280-day count assumes a 28-day cycle. If your cycle is 35 days, add 7 extra days. If it's 21 days, subtract 7. This adjustment ensures the due date accounts for when ovulation actually occurred.
Method 2: Conception Date
Formula: Due Date = Conception Date + 266 days
If you know your conception date (from ovulation tracking, IVF, or timed intercourse), add 266 days (38 weeks). Fertilization typically occurs within 24 hours of ovulation.
Trimester Breakdown
| Trimester | Weeks | Key Milestones |
|---|---|---|
| 1st Trimester | 1–13 | Positive test (week 4–5), heartbeat detectable (week 6–7), nuchal scan (week 11–14) |
| 2nd Trimester | 14–27 | Anatomy scan (week 18–22), movement felt, gender visible (week 18+) |
| 3rd Trimester | 28–40 | Viability (week 28), Group B Strep test (week 36), full term (week 37) |
Trimester Timeline Explained
A 40-week pregnancy is divided into three trimesters, each marked by distinct developmental stages and medical milestones:
First Trimester (Weeks 1–13)
The most critical period for organ development. Miscarriage risk is highest here (10–20% of known pregnancies). Morning sickness, fatigue, and breast tenderness are common. Your first prenatal visit, blood work, and nuchal translucency scan happen in this window.
Second Trimester (Weeks 14–27)
Many women feel their best during this period — nausea typically eases and energy returns. The anatomy scan (around week 20) checks fetal development in detail. You'll likely feel your first kicks (quickening) between weeks 18–24.
Third Trimester (Weeks 28–40)
The home stretch. Your baby gains weight rapidly, and you'll have more frequent prenatal visits. A baby born at 37 weeks or later is considered "full term." Your provider will monitor for signs of labor starting.
Worked Examples
Example 1: Standard 28-Day Cycle (LMP Method)
- • LMP: January 1, 2025
- • Cycle length: 28 days (no adjustment)
- • Due Date: January 1 + 280 days = October 8, 2025
- • 1st Trimester ends: April 2, 2025 (week 13)
- • 2nd Trimester ends: July 16, 2025 (week 27)
Example 2: Longer Cycle (35-Day Adjustment)
- • LMP: January 1, 2025
- • Cycle length: 35 days (+7 day adjustment)
- • Due Date: January 1 + 280 + 7 days = October 15, 2025
- • The longer cycle means ovulation (and likely conception) happened 7 days later
Example 3: Conception Date Mode
- • Conception date: January 14, 2025
- • Due Date: January 14 + 266 days = October 7, 2025
- • Note: This is close to Example 1 — conception at day 14 of a 28-day cycle is consistent with LMP Jan 1
Frequently Asked Questions
About This Calculator
Free pregnancy due date calculator. Enter your last period date or conception date to instantly find your baby's due date, gestational age, and trimester timeline.
Frequently Asked Questions
How is my due date calculated?
Your due date is calculated using Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If your cycle is longer or shorter than 28 days, the calculator adjusts accordingly.
What if I know my conception date instead?
Switch to "Conception Date" mode. The calculator adds 266 days (38 weeks) to your conception date to estimate your due date.
How accurate is the due date?
Only about 5% of babies are born on their exact due date. Think of your due date as the center of a 5-week window (weeks 38–42). Your provider will confirm with an ultrasound.
When do my trimesters start and end?
The first trimester runs weeks 1–13. The second trimester spans weeks 14–27. The third trimester begins at week 28 and ends at delivery.
Is this calculator a replacement for prenatal care?
No. This calculator provides an estimate only. Always consult your OB/GYN or midwife for confirmation via ultrasound.
Sarah brings a public health background to SuperCalc's health and fitness calculators. She translates clinical formulas into accessible tools backed by peer-reviewed research.
- MPH, Columbia University
- Former health data analyst at CDC
- Published health literacy researcher