Health & Fitness Calculators
Pregnancy Due Date Calculator
Estimate a due date from an entered last menstrual period using a transparent 280-day method.
Estimated due date will appear here
Enter an LMP date and calculate. No cycle length or hidden date method is applied.
What an estimated due date represents
The LMP convention counts 280 calendar days from the first day of the last menstrual period. It is a planning estimate, not pregnancy confirmation or a promise about the delivery date.
Worked example
For an entered LMP of January 1, 2025, adding 280 calendar days gives October 8, 2025. The calculation uses civil dates, so daylight-saving changes do not alter the result.
Clinical dating and limitations
The method assumes the entered LMP is known and suitable for dating. Irregular cycles, uncertain recall, assisted reproduction, and clinical information can change the obstetric estimate; ultrasound dating may differ.
Safety and trust
Pregnancy due dates are calendar estimates. This tool does not diagnose reproductive health, confirm pregnancy, or replace professional assessment.
Transparency note
Accuracy and limitations
Calzivo tools are built for practical estimates, conversions, and checks. Some tools use standard formulas or simplified assumptions, and results can be affected by input accuracy, rounding, units, local rules, or changing official requirements.
Health and fitness results are estimates, not medical advice. Formulas simplify real bodies and cycles, so important health decisions should be checked with a qualified clinician.
Reference check
Sources and references
These references provide background context for the topic. They do not replace official advice or documents for personal decisions.
- Methods for Estimating the Due Date
American College of Obstetricians and Gynecologists, Committee Opinion No. 700 (2017)
How to Use This Tool
Use these steps to enter the right inputs and interpret the result correctly.
Enter the first day of the last menstrual period.
Confirm that the date is not after the displayed validation date.
Select Calculate estimated due date to add exactly 280 calendar days.
Review the estimate and its clinical-dating limitations before copying it.
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Frequently Asked Questions
Common questions about Pregnancy Due Date Calculator and how to read the result.
Does this result confirm pregnancy?
No. It only adds 280 calendar days to an entered last menstrual period date and does not confirm pregnancy or establish clinical gestational age.
Why is cycle length not included?
This implementation uses one transparent ACOG-supported convention: 280 days from the first day of the last menstrual period. It does not silently add a cycle adjustment.
Can clinical dating produce another date?
Yes. Uncertain menstrual dates, irregular cycles, assisted reproduction, and clinical dating information such as ultrasound can lead to a different obstetric estimate.
Is the estimated date the actual delivery date?
No. It is a planning estimate, not a prediction of the actual delivery date.