Pregnancy Due Date Calculator
The Pregnancy Due Date Calculator estimates an expected date using the dating method selected on the page. Calendar estimates are approximate; a clinician may revise dating using cycle information, ultrasound, or other clinical context.
How to use this calculator
- Choose the dating method and enter the requested date exactly, then review the explanation of which timeline the estimate uses.
- Review the worked lmp example and compare its arithmetic with the inputs you plan to use.
- Change one input at a time when exploring a different scenario, and keep units and assumptions consistent.
Estimated due date
A common last-menstrual-period estimate adds 280 days (40 weeks) to the first day of the last menstrual period; other dating methods use different inputs.
- This convention assumes a typical 28-day cycle with ovulation around day 14, so it may not fit every cycle.
- The page's numerical output is calculated from the values entered; it does not independently verify whether those inputs fit the real-world situation.
Worked examples
LMP example
If the first day of the last menstrual period is 1 January, the 280-day estimate gives an approximate due date in early October.
LMP date + 280 calendar days = estimated due date
The calendar calculation estimates a due-date window from the selected starting date.
Understanding the result
The result is a planning estimate, not a confirmed delivery date.
Actual delivery timing varies, and cycle length, conception timing, and clinical findings can affect dating.
Important notes
Use prenatal care and a qualified clinician for pregnancy dates or health questions; do not rely on a calculator alone.
Displayed values may be rounded for readability. Keep appropriate precision for intermediate calculations and check the unit labels before using the result.
Frequently asked questions
What does the Pregnancy Due Date Calculator result mean?
The result is a planning estimate, not a confirmed delivery date.
What should I check before using the pregnancy due date calculator?
Use prenatal care and a qualified clinician for pregnancy dates or health questions; do not rely on a calculator alone.
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Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
- How to Calculate Age from a Date of Birth — Learn how exact age is calculated using years, months, and days rather than a rough year difference.
- How to Calculate Days Between Dates — Learn how date intervals work, including leap years and inclusive vs exclusive day counting.
- Percent Difference — Understand percent difference, when it is appropriate, and how it differs from percentage change and percent error.
This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.