Inputs
Due Date
This estimate assumes a standard 28-day cycle and should not replace medical advice.
Result
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Result explanation
How to read this result
Visualization
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Due Date Calculator
Estimate a pregnancy due date from the first day of the last menstrual period.
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Guide
Using the Due Date Calculator
What the calculator does
Open this calculator when you want to estimate a pregnancy due date from the first day of the last menstrual period.
It works best as a reference estimate you can compare against other inputs, habits, or professional guidance.
Formula and calculation explanation
Enter Last period date. Those values let the page estimate a pregnancy due date from the first day of the last menstrual period.
This calculator uses the first day of the last menstrual period as the starting point and adds the standard 280-day pregnancy length.
Estimated due date
\[Due\ Date = LMP + 280\ Days\]
This is the standard obstetric estimate used for a typical 40-week pregnancy.
Real-world examples
- Real-world setup: try last period date 2026-04-01 when you want to move from a rough question to a concrete scenario.
- What-if example: rerun the same setup with a different last period date to compare how much the headline answer moves.
Step-by-step walkthrough
- Enter Last period date.
- Double-check the calendar dates or times so the direction of the calculation matches what you want.
- Click Calculate Due Date. The calculator applies the method shown above and updates the answer instantly.
- Review the estimated due date and the supporting values for estimated conception date, then adjust one input at a time to compare scenarios cleanly.
FAQs
What does the estimated due date result mean?
The main result shown here is estimated due date. The calculator also returns estimated conception date so you can review the most useful supporting numbers at the same time.
Does this replace medical advice or diagnosis?
No. Health calculators are best used for rough planning and screening. They should support, not replace, individualized advice from a qualified professional.
Why might this calculator differ from another tool?
Different tools may use different reference formulas, rounding rules, or category cutoffs. This page uses the method explained in the formula section above.
Common mistakes
- Reversing the start and end values or forgetting that overnight spans may need special attention.
- Changing several inputs at once, which makes it harder to see which variable actually moved the result.
Edge cases
- Identical dates or times can produce a zero-length result, while reversed or overnight inputs may change how the span is interpreted.
- If a required field is left blank or contains an unsupported value, the calculator will not return a useful result until the input is corrected.
Interpretation of results
The main result shown here is estimated due date. The calculator also returns estimated conception date so you can review the most useful supporting numbers at the same time.
- Date results are calendar estimates, so they should be interpreted alongside the assumptions and date rules built into the page.
- The supporting metrics help you understand why the headline result looks the way it does and which tradeoffs sit behind it.
- When you compare scenarios, change one key input at a time so you can tie each output change back to a specific assumption.
Related concepts and calculators
Related ideas for this page include estimates, reference ranges, body metrics, inputs and assumptions, and screening.