← All free tools
Pregnancy Due Date Calculator
✓ 100% FREE — No Signup Needed
Enter the first day of your last period — your estimated due date, how far along you are, and your trimester dates appear instantly.
Based on Naegele's rule (LMP + 280 days, adjusted for cycle length). This is an estimate for planning — your doctor or midwife will confirm dating with an early ultrasound.
How the due date is calculated
Doctors count pregnancy as 40 weeks (280 days) starting from the first day of your last menstrual period — even though conception happens about two weeks later. This is called Naegele's rule. If your cycle is longer or shorter than 28 days, the estimate shifts: each extra cycle day pushes ovulation (and the due date) roughly one day later.
The three trimesters
- First trimester (weeks 1–13): the embryo becomes a fetus; organs begin forming. Fatigue and morning sickness are common.
- Second trimester (weeks 14–27): often called the "golden" trimester — energy returns, the bump shows, and you'll usually feel first kicks around week 18–22.
- Third trimester (weeks 28–40): rapid growth; the baby gains most of its weight. Regular check-ups track position and wellbeing.
How accurate is it?
Think of the due date as the middle of a range, not an appointment. Only about 1 in 20 babies arrives exactly on the date; most come within two weeks on either side. A first-trimester ultrasound measures the baby directly and is the most accurate way to date a pregnancy — it can shift the estimate by several days.
Frequently asked questions
How is a pregnancy due date calculated?
Doctors use Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period, adjusted for your average cycle length. This calculator applies it automatically.
What is Naegele's rule?
Naegele's rule estimates the due date as the first day of the last period plus one year, minus three months, plus seven days — equivalent to 280 days for a 28-day cycle.
How accurate is the due date?
It is an estimate: only about 5% of babies arrive exactly on their due date. Most are born within two weeks before or after. An early ultrasound gives the most accurate dating.
What are the three trimesters?
First trimester: weeks 1–13. Second trimester: weeks 14–27. Third trimester: weeks 28–40. Each brings different development milestones and symptoms.
Is this due date calculator free?
Yes. It is 100% free with no signup required.