Due Date Calculator
Estimate your due date using advanced dating methods, map your actual delivery window, and track your pregnancy milestones.
Calculation Method
Select how you want to date your pregnancy.
Calculate your timeline
Enter your dating information above to generate your customized pregnancy roadmap and delivery window.
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Pregnant
Pregnancy Roadmap
Delivery Window
Full Term RangeThe 40-Week Myth: Many healthy births happen before or after the estimated due date. As long as delivery occurs between Early Term (37 Weeks) and Postterm (42 Weeks), it is completely biologically normal.
Which date is more trustworthy?
ACOG guidelines explicitly support first-trimester ultrasound as the most accurate method to establish or confirm gestational age.
Important: If your calculator estimate differs from your doctor's ultrasound dating, always trust the clinical scan. Ultrasounds measure physical fetal growth rather than relying on calendar assumptions.
Biological Reality
Why your due date may change
It is extremely common for a doctor to adjust your due date during your pregnancy. This does not mean anything is wrong; it usually just means they received more accurate data.
Cycle length variations
If your cycle is 35 days instead of the assumed 28 days, you ovulated a week later. Your initial LMP-based due date will be a week early until corrected by a scan.
Dating method differences
Your last period, ovulation timing, and ultrasound scan do not always produce the exact same estimate. When they differ, doctors often use early ultrasound dating because it is usually more accurate.
First-Trimester Scans
If an early ultrasound shows the fetus measuring more than 5-7 days different than your LMP suggests, your doctor will permanently change your official due date to match the scan.
FAQ
Pregnancy Dating Questions
1Why do only 5% of babies arrive on their exact due date?+
A due date is simply a 40-week mathematical baseline, not a deadline. Normal, healthy pregnancies have a natural delivery window spanning from 37 weeks (Early Term) up to 42 weeks (Postterm).
2Which due date method is the most accurate?+
According to medical guidelines, a first-trimester ultrasound is the most accurate method to establish or confirm your due date. It measures the physical size of the fetus rather than relying on calendar assumptions.
3Why did my doctor change my due date?+
Doctors usually calculate your initial due date using your Last Menstrual Period (LMP). However, if an early ultrasound shows the fetus measuring significantly larger or smaller than the LMP timeline suggests, they will adjust your due date to match the ultrasound.
4Does cycle length affect my due date?+
Yes. Standard calculators assume every woman has a 28-day cycle and ovulates on Day 14. If your cycle is 35 days long, you likely ovulated a week later, meaning your true due date is a week later than standard LMP math suggests.
5What is the difference between fertilization and gestational age?+
Gestational age counts from the first day of your last period, meaning you are considered '2 weeks pregnant' when conception actually occurs. Fertilization age counts from the exact date of conception.
Next step
Deepen your understanding
If you want to understand exactly how pregnancy weeks are counted or why doctors use LMP instead of conception dates, read our guides.