Hijri Due Date Calculator: Step-by-Step Guide

Naegele's Rule in Hijri, Step by Step

Naegele's rule is the worldwide standard for calculating a due date, and it works in Hijri exactly as it does in the Gregorian calendar because it simply adds 280 days. The steps: first, identify the first day of your last menstrual period in the Hijri calendar. Second, add one full Hijri year to the year. Third, subtract three Hijri months from the month number. Fourth, add seven days to the day. The result is your expected due date.

A practical example: if the first day of your last period was 5 Ramadan 1447 AH, add one year to get 1448 AH, subtract three months from Ramadan (the ninth month) to reach Jumada al-Akhirah (the sixth month), then add seven days to 5 to get 12. The result: 12 Jumada al-Akhirah 1448 AH as your expected due date. Our calculator on the Hijri pregnancy page does this math automatically and also shows you the Gregorian date so you can compare it with hospital appointments.

An important note: if the subtraction lands on an impossible month number (for example, subtracting 3 months from Muharram), add 12 to the month number and subtract one year from the result. Example: last period on 10 Safar 1447 AH. Add one year: 1448 AH. Subtract 3 months from Safar (month 2): 2 - 3 = -1; add 12 to get 11 (Dhul-Qadah) and subtract one year to return to 1447 AH. Add 7 days: 17 Dhul-Qadah 1447 AH.

How to Convert Your Gregorian Date to Hijri

If you only know your last period date in Gregorian, convert it to Hijri first, then apply Naegele's rule. Accurate conversion uses the tabular Hijri calendar, which is based on a 30-year cycle and is precise enough for most medical and calculation purposes.

For a quick manual conversion, you can use the approximate formula: the Hijri year is roughly (the Gregorian year minus 622) multiplied by 33 and divided by 32. For 2026: 2026 - 622 = 1404, then 1404 x 33 / 32 = 1447.6, or about 1447-1448 AH. But this formula gives only the year, not the exact day and month, so it is better to use the conversion calculator on our site.

Very important: a calculated Hijri date may differ by a day or two from the official moon-sighting calendar. This is normal and medically acceptable because the due date itself is only an estimate. Only 4% of women deliver exactly on their calculated date; most deliver within two weeks before or after it.

Why Does Your Doctor's Calculation Sometimes Differ from Yours?

At the first ultrasound between weeks 8 and 12, the doctor measures the baby's crown-rump length and calculates gestational age far more accurately than LMP dating, especially if your cycles are irregular, you do not remember the date precisely, or you conceived while breastfeeding. In that case, the doctor relies on the ultrasound date and ignores the LMP calculation.

The accepted medical rule: if the early ultrasound dating differs from the LMP calculation by more than 7 days in the first trimester (or more than 10 days in the second trimester), the doctor adopts the ultrasound date and officially corrects the due date. If the difference is smaller, the LMP calculation stands. After the correction, the doctor usually does not change the date again, because bouncing between dates causes unnecessary confusion.

Practical advice: always record the first day of your last period accurately in your phone, get an early ultrasound between weeks 8 and 12 to confirm the date, then stick with the date your doctor set and ignore all other calculations completely.

Your Hijri Pregnancy Follow-Up Timetable, Month by Month

After calculating your due date, divide the pregnancy into the nine Hijri months to track it regularly. The first trimester covers roughly the first, second, and third months of pregnancy (through the end of week 13), the second trimester covers months four through six (weeks 14-27), and the third trimester covers month seven until delivery (weeks 28-40).

Write each doctor visit in the Hijri calendar in your notebook or phone so it matches government hospitals that use Hijri. Example: if your expected delivery is 12 Jumada al-Akhirah, your week 20 visit will fall around 12 Ramadan, and your week 28 visit around 12 Dhul-Qadah. This breakdown makes it easier to track regular checkups: the fifth-month ultrasound, the gestational diabetes screening between weeks 24 and 28, and growth monitoring in the final trimester.

Remember that pregnancy months in Hijri differ from Gregorian: pregnancy is 40 weeks, about 9 Gregorian months and 15 days, which equals about 9 Hijri months and 21 days because the Hijri year is about 11 days shorter. So do not be surprised if your doctor says you are in the seventh month while your Hijri count says late sixth; the difference is normal.

Common Mistakes in Hijri Pregnancy Dating

Mistake one: counting from ovulation day or the day of intercourse instead of the first day of the last period. Medically, pregnancy is dated from the first day of the last period because ovulation is hard to pinpoint, which adds a nominal two weeks before actual conception. If you count from ovulation, your due date will come out two weeks late.

Mistake two: forgetting that Hijri months are 29 or 30 days, not 30 or 31 like Gregorian months, so those who add 9 Gregorian months instead of doing the Hijri calculation get it wrong. Always use the Hijri month names and numbers when applying Naegele's rule.

Mistake three: relying on an imprecise memory of your last period date. A 5-day error in the period date means a 5-day error in the due date. Record dates as they happen, and if you are unsure, a first-trimester ultrasound is the answer.

Frequently asked questions