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CalcIntel

Pregnancy Due Date Calculator

Calculate your estimated due date based on the first day of your last menstrual period.

Your Age
36 years old

You are 36 years old, or 13,252 days since birth.

Years36
Months435
Weeks1,893
Days13,252
Data sources: CalcIntel Formula Library

Why This Calculation Matters

The Pregnancy Due Date Calculator turns a well-known health formula into an instant lookup. It's most useful when you're tracking a number over time or comparing yourself against published reference ranges from bodies like the CDC, NIH, or WHO. Use it as one data point among many, not a diagnosis.

How to Use This Calculator

  • Enter your values in the input fields, each one has a label and help text explaining what to type.
  • Results appear instantly as you type; there's no "calculate" button to press.
  • Change any input to compare scenarios side by side.

All math happens in your browser. Nothing you type is sent to a server, saved, or shared.

Reading Your Result

A single number tells you less than a trend. Track this value over weeks or months rather than obsessing over day-to-day variation. Hydration, sleep, and timing can all shift short-term readings without reflecting any real change.

Due Date Calculation

The most common method (Naegele's Rule) adds 280 days (40 weeks) to the first day of your last menstrual period (LMP).

Trimester Timeline

  • First trimester: Weeks 1-12
  • Second trimester: Weeks 13-27
  • Third trimester: Weeks 28-40

Only about 5% of babies are born on their exact due date. Most arrive within 2 weeks before or after.

When to Use This Calculator

  • Track personal health metrics over time alongside guidance from your clinician.
  • Understand how lifestyle changes may influence a given health number.
  • Compare values against recognized reference ranges from CDC, NIH, or WHO.

Limitations & Common Mistakes

  • Not a substitute for medical advice. Always consult a qualified clinician for anything that affects your care.
  • Population-level formulas don't account for individual medical history, medications, or body composition nuances.
  • Reference ranges evolve, use current CDC/NIH/WHO values when accuracy matters.

Frequently Asked Questions

How is my due date calculated?

The most common method adds 280 days (40 weeks) to the first day of your last menstrual period. Ultrasound dating in the first trimester is the most accurate method. Remember, a due date is an estimate, full-term delivery ranges from 37-42 weeks.

Should I use the Pregnancy Due Date Calculator for medical decisions?

No. This tool is educational. For anything affecting your health or treatment, consult a qualified clinician who can factor in your full medical history.

Which reference values does this use?

Where relevant, thresholds match CDC, NIH, or WHO guidance. Sources are linked in the "Sources & Further Reading" section below.

Is this calculator free to use?

Yes. The Pregnancy Due Date Calculator is free, requires no signup, and runs entirely in your browser, your inputs are never sent to a server.

How often is this calculator updated?

Formulas are reviewed against authoritative sources, and any rate or price data is refreshed on an automated schedule. Check the "as of" date on any live data panel for the most recent refresh.

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