Estimate your pregnancy due date and current gestational week
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Estimated due date
October 8, 2026
Current gestational age
32w 1d
Trimester
Trimester 3
StartEstimated due date
About 80% through pregnancy
Naegele's rule
Due date = LMP + 280 days
Naegele's rule adds 280 days (40 weeks) to the first day of your last menstrual period. It assumes a regular 28-day cycle; actual delivery may differ.
What is a due date calculator?
A due date calculator estimates when a baby is likely to be born from the first day of the last menstrual period (LMP). The most widely used method, Naegele's rule, adds 280 days — exactly 40 weeks — to that date. It also tells you how far along the pregnancy is right now, expressed in completed weeks and days and the current trimester. The estimate assumes a regular 28-day cycle; an early ultrasound gives a more individualized date, and only a small fraction of babies actually arrive on the predicted day.
How to use it
1. Enter the first day of your last menstrual period.
The calculator immediately shows the estimated due date (LMP + 280 days), your current gestational age in weeks and days, and which trimester you are in, along with a progress bar across the roughly 40-week pregnancy. If your cycle is much longer or shorter than 28 days, treat the result as approximate.
Formula and definition
Naegele's rule sets the estimated due date as:
Due date = LMP + 280 days (40 weeks)
Gestational age is the number of completed days since the LMP, shown as weeks and days. Pregnancy is divided into trimesters: the first runs through about week 12, the second from weeks 13–26, and the third from week 27 to birth. For example, an LMP of January 1, 2026 gives a due date of October 8, 2026.
Reading your results
The due date is an estimate, not a deadline — a full-term birth is anything from 37 to 42 weeks, and most babies arrive within two weeks of the predicted date. The gestational age tells you how the pregnancy is progressing and which milestones to expect, while the trimester frames typical symptoms and recommended check-ups. Because the calculation assumes a textbook 28-day cycle and a known LMP, your healthcare provider may revise the date after an ultrasound.
Frequently asked questions
How accurate is this due date? ▾
It is an estimate. Only about 1 in 20 babies arrives exactly on the due date; most are born within two weeks either side. An ultrasound dating scan is more accurate.
Why count from the last period instead of conception? ▾
The last menstrual period is an easily observed date, whereas the exact moment of conception is usually unknown. Gestational age is therefore measured from the LMP, about two weeks before conception.
My cycle isn't 28 days — does that matter? ▾
Yes. Naegele's rule assumes a 28-day cycle, so a notably longer or shorter cycle shifts the true date. Your provider may adjust based on cycle length or scan results.
What counts as full term? ▾
A pregnancy is considered full term from 37 to 42 weeks. Birth before 37 weeks is preterm and after 42 weeks is post-term; both warrant closer medical attention.
This tool provides a general estimate using Naegele's rule and is for informational purposes only — it is not medical advice. Always consult your doctor or midwife for an accurate due date and prenatal care.