Pregnancy Due Date Calculator Guide
Calculate pregnancy week from last menstrual period and understand date uncertainty.
What it does and when to use it
Estimated due date is often calculated as 40 weeks from the last menstrual period, but actual birth can happen across a wide range.
What information to enter
Enter last menstrual period or ultrasound date if supported. For irregular cycles, a clinician may adjust dating.
How to understand the result
The result shows pregnancy week and estimated due date. It is informational and does not replace medical follow-up.
Recommended step-by-step workflow
- Check the assumptionsEstimated due date is often calculated as 40 weeks from the last menstrual period, but actual birth can happen across a wide range.
- Use matching unitsEnter last menstrual period or ultrasound date if supported. For irregular cycles, a clinician may adjust dating.
- Compare with another scenarioThe result shows pregnancy week and estimated due date. It is informational and does not replace medical follow-up.
Formula at a glance
Short example
Why this matters
Estimated due date is often calculated as 40 weeks from the last menstrual period, but actual birth can happen across a wide range.
Step by step
- Define exactly what you want to calculate and which unit is correct.
- Enter values as they appear on a document, receipt, payslip or real measurement.
- Compare at least one extra scenario to see whether the result is sensitive to small input changes.
Numeric example
An LMP of January 1 gives an estimated due date around October 8 of the same year.
Mistakes to avoid
- Mixing numbers from different periods or units in one calculation.
- Ignoring assumptions, fees or limits the calculator cannot know by itself.
- Making a large decision from one result without testing a conservative scenario.
When to open the calculator
Open the calculator when you want to turn the explanation into a more exact number using your own inputs.
Common mistakes
- Mixing numbers from different periods or units in one calculation.
- Ignoring assumptions, fees or limits the calculator cannot know by itself.
Frequently Asked Questions
Is this a final answer?
Not always. It is a calculation or estimate based on the values entered.
What should I check before relying on it?
Check units, dates, fees and whether an important personal detail is missing.
Are my inputs saved?
No. The calculation runs in the browser and does not store your personal inputs.