Calculate your estimated due date, weeks pregnant, trimester, and conception date based on your last menstrual period (LMP) and cycle length.
First day of your last menstrual period (LMP)
Typical menstrual cycle length (21–45 days)
Enter values above to see results
This is an estimate only. Ultrasound measurements provide more accurate due dates. Always consult your healthcare provider.
Due Date = LMP + 280 days | Conception ≈ LMP + (Cycle Length − 14)LMPFirst day of Last Menstrual Period280 daysStandard gestational duration (40 weeks)Cycle Length − 14Days to ovulation (conception window)Naegele's rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period. Conception typically occurs around ovulation, which for a 28-day cycle falls on day 14. For cycles shorter or longer than 28 days, the conception estimate is adjusted accordingly.
Knowing your estimated due date is one of the first milestones of pregnancy. The due date helps you plan prenatal care appointments, prepare for the birth, and understand your baby's development milestones. This calculator uses Naegele's rule — the standard obstetric method — combined with your cycle length to provide a personalized estimate.
Enter the first day of your last menstrual period and your average cycle length. The calculator adds 280 days (40 weeks) to your LMP to determine the due date, estimates your conception date based on your cycle, and shows your current gestational age and trimester.
Naegele's rule: due date = first day of the last menstrual period + 280 days (40 weeks).
Estimated due date around 8 October; conception around 15 January.
Only about 4% of babies arrive on the exact due date — anywhere from 37 to 42 weeks is considered term.
The same 1 January LMP but a 32-day cycle.
This calculator keeps the due date at LMP + 280 days; only the conception estimate moves with cycle length.
Some clinicians adjust the due date for very long or short cycles — an ultrasound dating scan is more reliable than any formula.
Beyond the due date, this calculator shows your current trimester, weeks and days pregnant, and a developmental milestone for your current stage. This gives you an immediate sense of where you are in your pregnancy journey.
A common mistake is confusing gestational age (from LMP) with fetal age (from conception). Healthcare providers always use gestational age. Also, remember that the due date is an estimate — irregular cycles or late ovulation can shift the actual due date, which is why an early ultrasound is the gold standard for dating.
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