Pregnancy Due Date Calculator
Find your estimated due date, how many weeks pregnant you are today, and your trimester timeline, from the first day of your last period. Reviewed by Dr. Shalini B, our consultant obstetrician.
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Calculate your due date
Enter the first day of your last period. Adjust the cycle length if yours is not 28 days.
Nothing you enter is stored or sent anywhere. The calculation happens on your device.
How is a due date calculated?
The standard method, called Naegele's rule, takes the first day of your last menstrual period and adds 280 days, or 40 weeks. Pregnancy is counted from that first day, not from conception, which is why you are already considered about two weeks pregnant at the moment of conception. If your menstrual cycle is longer or shorter than the average 28 days, the date shifts, because you ovulate earlier or later, so this calculator adjusts for the cycle length you enter. The result is a well-established estimate, and it is the starting point every doctor uses until a scan refines it.
Why a dating scan is more accurate
The last-period method assumes a regular cycle and a known period date, which is not true for everyone. If your cycles are irregular, if you are unsure of your last period, or if you conceived soon after stopping contraception, the estimate can be off. An early ultrasound, usually the dating scan done in the first trimester, measures the baby directly and gives the most accurate due date. If your scan date differs from your period-based date, your doctor will usually go by the scan. Use this calculator to get your bearings, then let the scan confirm.
Your pregnancy in three trimesters
Pregnancy is divided into three trimesters, each with its own checks and milestones.
| Trimester | Weeks | What happens |
|---|---|---|
| First | 1 to 13 | Confirming pregnancy, dating scan, early blood tests, folic acid |
| Second | 14 to 27 | Anomaly scan, gestational diabetes screening, feeling movements |
| Third | 28 to 40 | Growth monitoring, position checks, birth planning |
Two checks in that list matter especially in India. Gestational diabetes screening in the second trimester is important because it is common and often silent, covered in our guide on gestational diabetes. And during monsoon, fever in pregnancy needs care, including dengue, covered in dengue in pregnancy.
"The first question in every early visit is the due date, and I always explain it is an estimate, not a deadline. What matters more than the exact day is starting antenatal care early, confirming the date with a scan, and keeping the checks on schedule, the dating scan, the anomaly scan, and the gestational diabetes test. A due date gives us a map. Good antenatal care is what keeps mother and baby safe along the way."
Dr. Shalini B, Consultant Obstetrician and Gynaecologist, Vivekananda Hospital, Begumpet
When to see a doctor
A due date is a reason to begin care, not to wait. Book your first antenatal visit as soon as you know you are pregnant, and seek prompt care for warning signs.
- Book early antenatal care once a home test is positive, ideally in the first trimester, to start folic acid, dating, and screening.
- Seek urgent care for bleeding, severe abdominal pain, a bad headache with swelling or vision changes, high fever, or reduced baby movements later in pregnancy.
- Do not wait for the due date if labour signs, regular painful contractions, waters breaking, or bleeding, start earlier.
Note: This calculator gives an estimate based on your last period and cycle length. It is an education aid, not a medical assessment, and does not replace a dating scan or antenatal care. Always confirm your due date and any concerns with your obstetrician.
Frequently Asked Questions
How is my due date calculated from my last period?
Your estimated due date is the first day of your last menstrual period plus 280 days, which is 40 weeks. This is called Naegele's rule. Pregnancy is counted from that first day, not from conception, so you are considered about two weeks pregnant at the time of conception. If your cycle is not 28 days, the date shifts, which is why this calculator adjusts for your cycle length.
How accurate is a due date calculator?
It gives a reliable estimate, but only about 1 in 20 babies arrive exactly on the due date. A normal birth can happen any time from about three weeks before to two weeks after it. The calculator assumes a regular cycle and an accurate last-period date, so an early dating scan, which measures the baby directly, gives the most accurate due date.
How many weeks pregnant am I?
Your weeks of pregnancy are counted from the first day of your last period to today. This calculator shows it for you in weeks and days once you enter your last period. Because dating is from the last period rather than conception, the number is usually about two weeks more than the time since conception. A scan confirms it accurately.
Does my cycle length change my due date?
Yes. The standard formula assumes a 28-day cycle with ovulation around day 14. If your cycle is longer, you ovulate later, so the due date moves later, and a shorter cycle moves it earlier. This calculator adjusts the estimate for the cycle length you enter. If your cycles are irregular, a dating scan is the most reliable way to set your due date.
What are the three trimesters of pregnancy?
The first trimester is weeks 1 to 13, when pregnancy is confirmed and dated and early screening begins. The second is weeks 14 to 27, which includes the anomaly scan and gestational diabetes screening, and when movements are often first felt. The third is weeks 28 to 40, focused on growth monitoring, the baby's position, and birth planning. Each has its own recommended checks.
When should I have my first antenatal visit?
As soon as a home pregnancy test is positive, ideally in the first trimester. An early visit starts folic acid, confirms and dates the pregnancy with a scan, checks your blood group and haemoglobin, and screens for conditions that are safest managed early. Starting antenatal care promptly matters more than the exact due date for keeping mother and baby healthy.
Can the due date change during pregnancy?
Yes. The period-based date is an initial estimate, and an early dating scan may adjust it. Doctors usually go by the scan date when it differs from the last-period date, especially with irregular cycles or an uncertain last period. Later scans assess growth rather than reset the due date. Once your date is confirmed early, it generally stays fixed for the rest of the pregnancy.
Where can I get antenatal care in Begumpet, Hyderabad?
Vivekananda Hospital, Begumpet offers full antenatal care with our consultant obstetrician Dr. Shalini B, including dating and anomaly scans, gestational diabetes screening, and delivery services on the same campus. Book on WhatsApp at +91 7207904418. Starting care early gives you the dating scan and first-trimester checks at the right time.
A Due Date Is the Start. Good Antenatal Care Is What Matters.
Begin your pregnancy care with our consultant obstetrician, dating scan, screening, and a clear schedule, all on one campus in Begumpet. Book an early visit and start on the right foot.
Address: Vivekananda Hospital, 6-3-871/A, Greenlands Road, Beside CM Camp Office, Begumpet, Hyderabad 500016
Also serving: Ameerpet, Prakash Nagar, Somajiguda, Punjagutta, Secunderabad, SR Nagar, Banjara Hills
About the Medical Reviewer
Dr. Shalini B (MBBS Gold Medal, DGO, DNB Obstetrics & Gynaecology, FMAS) is a Consultant Obstetrician and Gynaecologist at Vivekananda Hospital, Begumpet, Hyderabad, with experience across antenatal care, high-risk pregnancy, and minimal-access gynaecological surgery. NMC registration verifiable on the Indian Medical Register.
Medical disclaimer: This calculator and article are for general health information and education only. The due date is an estimate, not a medical assessment, and does not replace a dating scan or antenatal care. Always confirm your due date and any concerns with a qualified obstetrician. In an emergency, call +91 7207904418 or visit the nearest emergency department.
References: WHO, Maternal health | NHS, Due date and pregnancy dating | ACOG, Pregnancy stages and dating