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Pregnancy Calculator - Due Date and Week Calculator

How the Pregnancy Calculator Works

Due Date = Last Menstrual Period (LMP) + 280 days (Naegele's Rule)

This calculator uses Naegele's Rule, a medically established method for estimating the expected due date. Pregnancy is counted from the first day of your last menstrual period (LMP), with 280 days (40 weeks) added to calculate the estimated delivery date. This method is used by healthcare providers worldwide as the standard approach for pregnancy dating.

  1. 1

    Enter Your LMP Date

    Input the first day of your last menstrual period - this is the starting point for all pregnancy calculations

  2. 2

    Calculate Pregnancy Duration

    The calculator determines how many weeks and days have passed since your LMP to establish your current stage

  3. 3

    View Pregnancy Details

    Receive your estimated due date, current trimester, and appropriate weight gain recommendations for your stage

Use Cases

Personal Pregnancy Tracking

Expecting mothers use this to monitor their pregnancy week by week and follow their baby's developmental milestones

Delivery Planning

Plan for maternity leave, arrange childcare for other children, and prepare supplies well in advance of your due date

Healthcare Coordination

Medical clinics use LMP-based calculations as an initial estimate before confirming gestational age with ultrasound

Weight Management

Track appropriate weight gain for each trimester to support healthy fetal development and maternal health

Tips

  • 1

    Record your last menstrual period date as soon as you discover your pregnancy - it is essential for accurate calculations

  • 2

    Remember that the due date is an estimate - only about 5% of babies are born on their exact due date

  • 3

    Use this calculator for personal tracking but rely on ultrasound confirmation from your healthcare provider

  • 4

    Consult your doctor if your menstrual cycles are irregular for more precise dating methods

Common Mistakes

  • Confusing conception date with last menstrual period date - pregnancy is calculated from the LMP, not conception

  • Worrying excessively if delivery does not occur on the exact due date - this is completely normal

  • Not remembering the menstrual period date accurately, leading to less precise calculations

  • Relying solely on calculator estimates without regular prenatal medical care and ultrasound confirmation

FAQs

How accurate is the calculated due date?

The due date is an estimate based on the average pregnancy duration of 40 weeks. Most deliveries occur between weeks 38 and 42, which is considered full term. A first-trimester ultrasound typically provides the most accurate due date estimate.

What if my menstrual periods are irregular?

If your cycles are irregular, LMP-based calculations may be less accurate. In such cases, early ultrasound dating is the preferred method for determining gestational age and estimating your due date more precisely.

How do I calculate if I do not remember my LMP date?

Try to recall any events or circumstances that might help you remember the approximate date. If you cannot remember, an early ultrasound can accurately determine gestational age based on fetal measurements.

When is each trimester and what happens during them?

The first trimester spans weeks 1-12 and involves major organ formation. The second trimester (weeks 13-27) is when you may feel fetal movement and experience less nausea. The third trimester (weeks 28-40) involves rapid fetal growth and final preparations for birth.

Related tools

Pick another tool to continue your calculation.

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Pregnancy Due Date Calculator

Calculate estimated due date from last menstrual period.

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Pregnancy Week Calculator

Calculate current pregnancy week and stage.

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Dog Pregnancy Calculator

Calculate dog due date

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Pregnancy Calorie Calculator

Calculate recommended calories during pregnancy.

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Pregnancy Weight Gain Calculator

Calculate recommended weight gain during pregnancy.