Family
Pregnancy Due Date Calculator
- Browser-based
- No signup
Estimate a due date from the first day of the last menstrual period or a conception date. Optional cycle length adjusts the LMP estimate. See gestational age, trimester, countdown, and progress. Educational only—not medical advice.
100% Client-Side
Your data never leaves your computer.
How to use this tool
1. Enter the first day of your last menstrual period or conception date as prompted. 2. Adjust cycle length if that field is shown. 3. Click Calculate. 4. Review estimated due date and current gestational week. 5. Confirm with your healthcare provider—only clinical dating is definitive.
Worked example
Example: LMP 1 January with a 28-day cycle estimates a due date around early October—ultrasound dating may differ.
How it works
Enter the first day of the last menstrual period (LMP) or a conception date. For LMP, an optional cycle length adjusts Naegele’s rule (280 days from LMP on a 28-day cycle). The calculator estimates due date, gestational age, trimester, and days remaining. Results are educational estimates only and are not medical advice.
Limitations
This tool provides a general estimate for educational purposes and is not medical advice. Due dates are estimates only. Consult a qualified healthcare professional for personal guidance.
Privacy and file handling
Your data is processed in your browser and is not uploaded to our server.
Accuracy & methodology
This section documents how the calculator works, what it leaves out, and when results were last reviewed. Figures are educational estimates—not professional advice—and are not labeled "current" unless tied to automatically updated reference data.
- Formula source or methodology
- From LMP: due date = LMP + 280 days adjusted for cycle length (default 28 days). From conception: due date = conception + 266 days. Gestational age counted from estimated LMP; trimesters at 13 and 27 weeks.
- Jurisdiction
- Obstetric dating conventions (general; not a country-specific clinical protocol)
- Unit system
- Calendar dates (ISO YYYY-MM-DD)
- Rounding method
- Whole days and completed weeks for gestational age
- Assumptions
- Regular cycle adjustment via user-entered cycle length (21–45 days)
- Single fetus; spontaneous pregnancy dating conventions
- Calendar dates without time-of-day
- Known omissions
- Not medical advice. Does not diagnose, treat, or replace clinical assessment.
- Ultrasound dating or IVF transfer-day adjustments
- Irregular cycles beyond the cycle-length field
- Multiple gestation and pregnancy complications
- Test cases (automated)
- LMP 2026-01-01 with 28-day cycle → due date 2026-10-08
- Future LMP relative to as-of date is rejected
- Version & last verified
Logic version 1.0. Content and formulas last verified .
Frequently asked questions
How is the due date calculated?
From the last menstrual period (LMP), the estimate uses 280 days for a 28-day cycle, adjusted by cycle length. From conception, it uses 266 days.
What is gestational age?
Gestational age is counted from the estimated LMP in weeks and days, and is used to determine the trimester and progress percentage.
Is this medical advice?
No. Results are educational estimates only. Confirm dates and care plans with a qualified healthcare professional.
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