Updated · Methodology: named formula library
Pregnancy Due Date Calculator
Calculate your estimated due date based on the first day of your last menstrual period.
You are 36 years old, or 13,252 days since birth.
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 does the Pregnancy Due Date Calculator work?
Enter your birth year (default: 1990) and any other inputs; the calculator instantly applies its pregnancy due date formula and shows the result with details. All math runs in your browser; nothing is sent to a server.
Is the Pregnancy Due Date Calculator accurate for pregnancy decisions?
It uses standard, documented formulas that match published references. For high-stakes pregnancy decisions, verify the result against an authoritative source (industry calculator, professional advisor, or government data). The calculator is a planning estimate, not a substitute for professional judgment.
What inputs does the Pregnancy Due Date Calculator require?
3 inputs: Birth Year, Birth Month, Birth Day. Each has a sensible default; replace with your own values to get a result tailored to your situation.
Can I bookmark or share the Pregnancy Due Date Calculator?
Yes — the URL is stable: https://www.calcintel.com/calculator/pregnancy-due-date. Inputs reset to defaults on each visit (no input is stored), so screenshot or copy the result if you want to preserve a specific scenario.
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Source: BLS Consumer Price Index, 2026.