What is LMP and why is it used?

LMP stands for Last Menstrual Period. Healthcare providers use the first day of your LMP to calculate gestational age and due date because it is easy to identify and typically occurs about two weeks before conception. This means the standard 40-week pregnancy count begins before conception actually takes place.

How accurate is a due date calculator?

A due date based on LMP is an estimate. Only about 5% of babies are born on their exact due date. Most births occur within two weeks before or after the due date. An early ultrasound (especially before 14 weeks) provides a more accurate due date by measuring the size of the embryo.

What is the difference between gestational age and fetal age?

Gestational age is counted from the first day of your LMP and is the standard used in obstetrics. Fetal age (or embryonic age) counts from actual conception, which typically occurs about two weeks after LMP. Gestational age is about 2 weeks more than fetal age.

When should I see a doctor after a positive pregnancy test?

Schedule your first prenatal visit as soon as you confirm pregnancy, ideally between weeks 8 and 10. Early prenatal care is important for monitoring the health of both mother and baby and confirming the due date via ultrasound.

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Pregnancy Due Date Calculator

Calculate your estimated due date, weeks pregnant, trimester, and conception date based on your last menstrual period (LMP) and cycle length.

pregnancydue dateLMPweeks pregnanttrimesterconception

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Enter Values

First Day of Last Menstrual Period (LMP)*

First day of your last menstrual period (LMP)

Average Cycle Length(days)*

Typical menstrual cycle length (21–45 days)

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Results

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)

Variables

LMPFirst day of Last Menstrual Period

280 daysStandard gestational duration (40 weeks)

Cycle Length − 14Days to ovulation (conception window)

Explanation

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.

What is the Pregnancy Due Date Calculator?

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.

How to Use This Calculator

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.

Why Use MyCalculatorsHub's Due Date Calculator?

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.

Common Mistakes to Avoid

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.