Free Pregnancy Due Date Calculator Online
Due date via Naegele's Rule with milestone tracker
This calculator estimates your baby's due date using Naegele's Rule — the standard obstetric formula that adds 280 days (40 weeks) to the first day of your last menstrual period. Alongside the estimated due date, it shows key pregnancy milestones by trimester so you know what to expect at each stage.
Frequently Asked Questions
About the Pregnancy Due Date
Naegele's Rule has been the standard method for calculating due dates since the 1800s, named after German obstetrician Franz Karl Naegele. The rule assumes a 28-day cycle with ovulation on day 14 — which is an average, not a universal reality. Women with longer or shorter cycles may have due dates that differ slightly from this calculation.
The 40-week timeline is counted from the LMP, not from conception. Since ovulation typically occurs about 14 days into the cycle, fertilization usually happens around the start of week 3. This means a fetus is actually about 38 weeks old at the time of a "40-week" due date.
Most healthcare providers confirm the due date with an early ultrasound (before 14 weeks), which can measure fetal crown-to-rump length to give a more accurate gestational age estimate. The LMP-based calculation and ultrasound measurement together give the most reliable due date.
Formula Used
EDD = LMP + 280 days (40 weeks)
Naegele's Rule: LMP + 1 year - 3 months + 7 days
When Should You Use This?
The Pregnancy Due Date is ideally suited for fitness enthusiasts, healthcare professionals, and individuals monitoring their health who need to perform quick, accurate calculations related to general calculations. Use this tool when you need to verify figures, compare different scenarios, or get a precise answer without manual computation errors.
What Does The Result Mean?
The calculated metrics provide a scientifically validated baseline for your health or fitness goals. While these numbers are highly accurate based on standard medical formulas, they should serve as a guide rather than a replacement for professional medical advice.
Example Calculation
Calculating due date from last menstrual period
📥 Inputs
- Last Menstrual Period (LMP): March 10, 2025
- Average cycle length: 28 days
🔢 Calculation Steps
- 1Apply Naegele's Rule: LMP + 280 days
- 2March 10, 2025 + 280 days = December 15, 2025
- 3Alternative method: LMP + 1 year − 3 months + 7 days
- 4= March 10, 2026 − 3 months + 7 days = December 17, 2025 (minor rounding difference)
- 5First trimester ends: ~June 16, 2025 (week 12)
- 6Second trimester ends: ~September 22, 2025 (week 27)
- 7Full term window: November 24 – December 29, 2025 (37–42 weeks)
Limitations of this Calculator
- Formulas are based on population averages and may not perfectly reflect individuals with extreme muscle mass or atypical body compositions.
- Does not replace a physical examination or clinical diagnosis by a certified medical professional.
- Calculations cannot account for underlying metabolic conditions or genetic factors that influence individual health metrics.
How to Use the Pregnancy Due Date
- 1Enter your values into the Pregnancy Due Date input fields above.
- 2Review the input labels to ensure you are using the correct units.
- 3Click the "Calculate" button to get your instant result.
- 4Use the step-by-step breakdown to understand how the result was calculated.
- 5Export or copy your result to use in reports or share with others.
Tips & Best Practices
- Only ~5% of babies arrive on their exact due date. A 'normal' full-term delivery is 37-42 weeks.
- Double-check your input units before calculating — using the wrong unit is the most common source of errors.
- Bookmark this Pregnancy Due Date for quick access next time you need it.
- Use the share button to send your results to a colleague or save them for later reference.
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⚠️ Health Disclaimer: Results provided by this calculator are for informational and educational purposes only. They do not constitute medical advice. Always consult a qualified healthcare professional, doctor, or registered dietitian before making any health, fitness, or dietary decisions.