How accurate is Naegele's rule?

It's a standard estimate assuming a 28-day cycle with ovulation on day 14 — only about 5% of babies actually arrive on the exact calculated date. Your healthcare provider may adjust the date using an ultrasound, which is more accurate for irregular cycles.

What if my cycle isn't 28 days?

Naegele's rule assumes a 28-day cycle. If yours is longer or shorter, the real due date shifts accordingly — your provider can adjust for this, especially with early ultrasound dating.

Why does an ultrasound give a more accurate estimate?

An early ultrasound measures the fetus directly, which accounts for individual variation in cycle length and ovulation timing that a simple date-based formula can't capture — this is why providers often adjust the calculated due date after an early scan.

Is this calculator a substitute for prenatal care?

No — this is a quick reference estimate, not medical guidance. Follow your healthcare provider's assessment and prenatal care schedule, which accounts for far more than just the last menstrual period date.

Why does the due date matter if most babies don't arrive exactly then?

It's still a useful planning reference point — for tracking pregnancy milestones, scheduling prenatal visits, and understanding roughly which trimester you're in, even though the exact delivery date naturally varies.

Health & Fitness Cluster

Pregnancy Due Date Calculator

Estimate due date and current week using Naegele's rule.

TL;DR: Pregnancy Due Date Calculator is a free, browser-based tool that lets you estimate due date and current week using Naegele's rule.

First day of last menstrual period

What Is the Pregnancy Due Date Calculator?

The Pregnancy Due Date Calculator computes health and physiological metrics based on established clinical formulas, helping you monitor fitness benchmarks, body composition, and daily nutritional requirements.

Step-by-Step: Using This Calculator

Select your measurement system (Metric or Imperial units).
Enter your height, weight, age, and relevant biometric measurements.
View your calculated biometric score and clinical classification category.
Use the target recommendations to guide sustainable fitness and wellness goals.

Mathematical Formula & Methodology

Here is the standard mathematical equation used to calculate this result accurately:

\text{Naegele's Rule: } \text{Due Date} = \text{First Day of Last Menstrual Period (LMP)} + 1 \text{ Year} - 3 \text{ Months} + 7 \text{ Days}

Formula Variables Explained:
Estimates expected date of delivery (EDD) and current gestational age in weeks and days based on standard 280-day gestation.

Step-by-Step Worked Example

LMP on May 10, 2025 gives an estimated due date of February 17, 2026.

Maximize Your Results

Track Long-Term Trends: Measure biometrics under consistent conditions (e.g., first thing in the morning) rather than stressing over daily fluctuations.
Holistic Context: Treat formula calculations as broad wellness guidelines rather than strict medical diagnoses.
Consult Professionals: Consult a physician or registered dietitian before making substantial dietary or caloric adjustments.

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100% Client-Side Privacy Guarantee

All processing runs locally inside your browser using JavaScript and HTML5 APIs. Your data, files, and inputs are never uploaded to any remote server. Complete privacy by design.

Frequently Asked Questions

: It's a standard estimate assuming a 28-day cycle with ovulation on day 14 — only about 5% of babies actually arrive on the exact calculated date. Your healthcare provider may adjust the date using an ultrasound, which is more accurate for irregular cycles.
: Naegele's rule assumes a 28-day cycle. If yours is longer or shorter, the real due date shifts accordingly — your provider can adjust for this, especially with early ultrasound dating.
: An early ultrasound measures the fetus directly, which accounts for individual variation in cycle length and ovulation timing that a simple date-based formula can't capture — this is why providers often adjust the calculated due date after an early scan.
: No — this is a quick reference estimate, not medical guidance. Follow your healthcare provider's assessment and prenatal care schedule, which accounts for far more than just the last menstrual period date.
: It's still a useful planning reference point — for tracking pregnancy milestones, scheduling prenatal visits, and understanding roughly which trimester you're in, even though the exact delivery date naturally varies.

Cite This Tool

Referencing this tool in a paper, article, or bibliography? Copy a ready-made citation below.

NexLove.org. (2026). Pregnancy Due Date Calculator [Software]. https://nexlove.org/tools/pregnancy-due-date-calculator.html

“Pregnancy Due Date Calculator.” NexLove.org, 2026, nexlove.org/tools/pregnancy-due-date-calculator.html.

NexLove.org (2026) Pregnancy Due Date Calculator. Available at: https://nexlove.org/tools/pregnancy-due-date-calculator.html (Accessed: 2026).

@misc{nexlove_pregnancy_due_date_calculator,
  title = {Pregnancy Due Date Calculator},
  author = {{NexLove.org}},
  year = {2026},
  url = {https://nexlove.org/tools/pregnancy-due-date-calculator.html}
}

Embed This Tool

Add the live Pregnancy Due Date Calculator tool to your own website with this snippet — it loads the real, working tool in an iframe, not a static screenshot.

<iframe src="https://nexlove.org/embed/pregnancy-due-date-calculator.html" width="100%" height="600" style="border:1px solid #e2e8f0;border-radius:12px" title="Pregnancy Due Date Calculator — NexLove.org" loading="lazy"></iframe>

Understanding the Pregnancy Due Date Calculator

This calculator provides instant, client-side computations designed for precision and ease of use.

Key Benefits

Instant Execution: No page reloads required. The math is calculated dynamically as you type.
Private & Secure: No financial, personal, or numerical data is transmitted. All calculations run in your browser's memory.

Disclaimer: While we strive for absolute accuracy, the Pregnancy Due Date Calculator should be used for informational purposes. Always verify critical calculations with a licensed professional where applicable.

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