Enter the first day of your last period in Gregorian or Hijri to see your estimated due date and how far along you are today.
Today
Pregnancy calculator result
Estimated due date
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Pregnancy today
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Days until the due date
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Estimated conception
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Second trimester starts
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Third trimester starts
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These are estimates using Naegele’s rule (280 days from the first day of the last period). Your doctor sets the most accurate date by ultrasound; this calculator does not replace medical care.
Enter the first day of your last period, in Gregorian or Hijri.
Choose your cycle length if it differs from 28 days.
Press “Calculate due date” to see the results in both calendars.
How the results are calculated
Result
Method
Estimated due date
First day of last period + 280 days (+ cycle length − 28)
Pregnancy today
Days from the first day of the last period to today, in weeks and days
Estimated conception
14 days after the first day of the last period (28-day cycle)
Second trimester
At 14 completed weeks
Third trimester
At 28 completed weeks
Trimesters
Trimester
Weeks
First
From the start of pregnancy to the end of week 13
Second
Week 14 to the end of week 27
Third
Week 28 to birth
Important
This calculator gives estimates only and is not medical advice. Doctors usually date a pregnancy by an early ultrasound scan; if your doctor’s date differs from the calculator, use your doctor’s date.
To find a date a number of days or weeks ahead, use the Date Calculator; for the time between two dates, use Date Difference.
Last updated:
Frequently asked questions
How is the due date calculated?
With Naegele's rule, which adds 280 days (40 weeks) to the first day of the last menstrual period. If the last period started on 1 January 2026, the estimated due date is 8 October 2026.
How many weeks does a pregnancy last?
40 weeks counted from the first day of the last period, which is about 38 weeks from conception in a regular 28-day cycle.
When do the second and third trimesters start?
The second trimester starts at 14 completed weeks and the third at 28 completed weeks; the calculator shows the date of each.
Can I enter a Hijri date?
Yes. Choose Hijri in the date field and enter the first day of your last period; the results are shown in both the Hijri (Umm al-Qura) and Gregorian calendars.
What if my cycle is longer or shorter than 28 days?
Choose your cycle length and the due date moves by the difference from 28 days. With a 35-day cycle it moves 7 days later, to 15 October 2026 instead of 8 October in the example above. If your cycle is irregular, your doctor's ultrasound date is more accurate.
Is the due date exact?
It is only an estimate; birth can happen before or after it. A birth from the start of week 37 to the end of week 41 is considered full term, and your doctor sets the most accurate date and follows the pregnancy.