Your due date, week by week.
Enter the first day of your last menstrual period and see your estimated due date instantly, along with your current week of pregnancy, trimester, estimated conception date and how many days remain until you meet your baby.
Your dates
The first day of your last menstrual period.
Your average menstrual cycle length in days.
Naegele's rule adds 280 days (40 weeks) to the first day of your last period. If your cycle is longer or shorter than 28 days, the due date shifts by the difference. Results update as you type.
What this stage means
Where you are on the pregnancy timeline
Milestone dates for your pregnancy
Key weeks and typical checkups
Every row is calculated from your last period date. The highlighted row is the closest to where you are right now.
| Week | Approx. date | What typically happens |
|---|
Pregnancy dating, explained
How Due Dates are Calculated
Due dates are calculated using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If your cycle length differs from the standard 28 days, an adjustment is made by adding or subtracting the difference. Only about 5% of babies are born on their exact due date.
Understanding Pregnancy Trimesters
Pregnancy is divided into three trimesters. The first trimester (weeks 1-12) involves major organ development. The second trimester (weeks 13-26) is often called the "golden period" with reduced nausea and visible growth. The third trimester (weeks 27-40) focuses on fetal weight gain and preparation for birth.
Key Milestones by Week
Week 6: heartbeat detectable. Week 12: all organs formed. Week 16: sex may be visible on ultrasound. Week 20: halfway point, anatomy scan. Week 24: viability milestone. Week 28: eyes open. Week 37: considered early term. Week 39-40: full term. Week 42: post-term, induction usually recommended.
When to See a Doctor
Schedule your first prenatal visit within 8 weeks of your last period. Regular prenatal care typically includes monthly visits until week 28, biweekly visits from weeks 28-36, and weekly visits from week 36 until delivery. Seek immediate care for heavy bleeding, severe pain, or decreased fetal movement.
Common questions
How accurate is the due date calculation?
Due date estimates based on LMP are accurate within about two weeks. Only 5% of babies arrive on their exact due date. Most births occur between 38 and 42 weeks. An early ultrasound (before 12 weeks) can provide a more precise estimate.
What if my cycle is irregular?
If your cycle length varies significantly, LMP-based due dates may be less accurate. An early ultrasound measurement is the best way to establish your due date with irregular cycles. This calculator adjusts for cycle length if different from 28 days.
What is gestational age vs fetal age?
Gestational age counts from the first day of your last period, making the "pregnancy" start about two weeks before conception. Fetal age counts from actual conception, approximately 2 weeks less than gestational age. Medical professionals use gestational age.
Can I change my due date?
Your healthcare provider may adjust your due date based on ultrasound measurements, especially if they differ significantly from the LMP calculation. First-trimester ultrasounds are most accurate for dating. Once established, the due date should not be changed unless there is a significant discrepancy.
This calculator gives an estimate, not a medical diagnosis. Only about 5% of babies arrive on their exact due date, and LMP-based dating can be off by two weeks or more, especially with irregular cycles. Your exact due date is determined by your gynecologist or obstetrician, usually with an early ultrasound. Always follow the guidance of your prenatal care provider, and seek immediate care for heavy bleeding, severe pain or decreased fetal movement.