Health & Fitness Calculators
Pregnancy Due Date Calculator
Estimate your baby's due date.
Calculation assumptions
- *This estimate uses an LMP-based due-date method adjusted by cycle length.
- *Due dates are planning estimates, not exact predictions of birth day.
- *Ultrasound findings and clinician guidance can shift the final dating.
- *This result is not medical advice and should not be used to diagnose, treat, prevent, or manage a medical condition.
Enter your values and press Calculate.
Results and breakdowns will appear here after a valid calculation.
How Due Dates are Estimated
Most due-date estimates start with the first day of the last menstrual period and add about 280 days. This calculator adjusts that date by your average cycle length.
Example: if the first day of the last period was January 1 and the average cycle length is 28 days, the estimated due date is October 8.
Safety notes and common mistakes
Due dates are estimates. Actual delivery can happen before or after the estimate, and ultrasound or clinician dating may be more specific.
- Do not treat the date as a guaranteed delivery day.
- Do not use this result as pregnancy confirmation.
- Do not ignore irregular cycles, uncertain dates, bleeding, pain, or pregnancy concerns.
- Use professional guidance for pregnancy questions, symptoms, or medical concerns.
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.
How to Use This Tool
Use these steps to enter the right inputs and interpret the result correctly.
Select the first day of your last menstrual period.
Adjust the slider for your average cycle length.
The calculator will estimate your due date and current progress.
Related Tools
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Related Guides
Background reading and explanations related to Pregnancy Due Date Calculator.
Ovulation and Fertile Window Explained
Learn what ovulation and the fertile window usually mean and why both are cycle-based estimates.
Menstrual Cycle Length Explained
Understand cycle length, day 1, and why regular and irregular cycles affect planning estimates.
Due Date Calculation Methods
See how LMP-based due date estimates work and why cycle length can shift the timeline.
Frequently Asked Questions
Common questions about Pregnancy Due Date Calculator and how to read the result.
How accurate is this date?
Only about 4% of babies are born on their exact due date. Most are born within a week before or after.
What method does this calculator use?
It uses a last-menstrual-period estimate of about 280 days, adjusted by average cycle length.
Can ultrasound change the due date?
Yes. Ultrasound measurements and clinician review can shift or refine pregnancy dating.
Can I use a future last-period date?
No. The last period date should be today or in the past.
Is this medical advice?
No. It is an estimate for planning and should not be used to diagnose, treat, prevent, or manage a medical condition.
What if my cycle is irregular?
Irregular or uncertain cycle dates can make LMP-based due-date estimates less reliable. Use professional guidance if timing matters.