What is Pregnancy Due Date Calculator?
This calculator estimates a due date by adding 280 days, or 40 weeks, to the first day of the last menstrual period (LMP). This is the implemented form of Naegele's rule.
An estimated due date is a clinical reference point, not a prediction of the exact birth date. LMP uncertainty, irregular cycles, assisted reproduction, and ultrasound findings can change pregnancy dating.
Why Use This Tool?
The estimate can provide an initial date for discussion with a prenatal care professional. Clinical dating should use complete history and applicable ultrasound or assisted-conception information.
How Does This Tool Work?
Enter a valid LMP date. The implementation creates a local date at noon, adds exactly 280 calendar days, and returns an ISO-style year-month-day date.
Estimated due date = first day of LMP + 280 days.
- LMP
- First day of the last menstrual period, as entered.
- 280 days
- Forty weeks counted from LMP, not from conception.
Understanding Your Results
The calculation assumes a conventional cycle and reliable LMP. A clinician may establish or revise the estimated due date using ultrasound and professional criteria. Do not use this page to assess viability, gestational complications, or when delivery should occur.
Why Tracking This Matters
Accurate dating supports prenatal care timing, but symptoms matter more than a calculated date. Bleeding, severe pain, fainting, breathing difficulty, or other urgent concerns require prompt medical care.
Benefits of Using Pregnancy Due Date Calculator
- Simple 280-day estimate
- Transparent LMP basis
- Private date arithmetic
- Clear need for clinical confirmation
How Is the Result Calculated?
If LMP begins January 15, adding 280 days yields the calculator's estimated date. The result may differ from clinical dating and does not identify conception date.
Tips for Better Results
- Enter the first day, not the last day, of the period.
- Tell the clinician if cycles are irregular or LMP is uncertain.
- Use assisted-reproduction dates when instructed by the treating team.
- Begin prenatal care based on professional guidance.
Standards and References
Conclusion
Use the date as an initial estimate only and arrange qualified prenatal care for confirmation, monitoring, and any symptoms.