You will get the current week, due date and trimester dates — for example: 24 w 3 d, due Jan 15.
This calculator estimates the due date (EDD), the current gestational week and the trimester from the first day of your last period or the conception date. It’s a calendar guide, not a medical conclusion: the exact gestational age is set by your doctor, usually with a first-trimester ultrasound.
How the due date is calculated
- From the last period (Naegele’s rule): EDD = first day of the last period + 280 days (40 weeks). With a cycle longer or shorter than 28 days, the date shifts by the difference.
- From the conception date: EDD = conception + 266 days. The gestational age is counted about 2 weeks ahead of the embryonic age, because it starts from the period, not conception.
- Pregnancy is divided into trimesters: 1st — weeks 1–13, 2nd — 14–27, 3rd — 28–40.
Weeks and trimesters
A short map of pregnancy by week. Remember: the timings are approximate — every pregnancy runs its own course.
| Period | Weeks | What happens |
|---|---|---|
| 1st trimester | 1–13 | All organs and systems form; by the end the baby is ~7 cm |
| 2nd trimester | 14–27 | Rapid growth, first movements (usually weeks 18–22) |
| 3rd trimester | 28–40 | Weight gain, lung maturation, preparing for birth |
| Full term | 37–42 | Birth within this window is considered normal |
Due date FAQ
How accurate is the due date?
Only about 5% of babies arrive exactly on their due date. The EDD is the middle of a window: birth from week 37 to 42 is considered normal. Plan for “plus or minus two weeks”, not a specific day.
My cycle isn’t 28 days — what should I do?
Enter your cycle length — the calculator shifts the date by the difference. With an irregular cycle the calendar method is less reliable, and a first-trimester ultrasound dates the pregnancy more precisely.
What’s the difference between gestational and embryonic age?
Gestational age is counted from the first day of the last period, embryonic age from conception. Gestational age is about 2 weeks ahead. Doctors and all pregnancy references use the gestational age — and so does this calculator.
Why did the ultrasound show a different date?
A first-trimester ultrasound measures the embryo and dates the pregnancy more precisely than the calendar, especially with an irregular cycle. If the dates differ, follow your doctor’s conclusion.