Pregnancy Due Date Calculator

Baby Due Date Calculator: Core Features and Principles

Can't remember the exact date of your last period or struggling to estimate when your baby will be born? By entering the first day of your Last Menstrual Period (LMP), this tool automatically calculates your Estimated Due Date (EDD). It uses the classic Naegele's Rule: Due Date = LMP + 280 days (40 weeks). The calculator not only provides your Gregorian due date but also converts it into the corresponding lunar date and day of the week. It calculates exactly how far along you are and how many days are left until your due date, giving you a clear pregnancy timeline.

Why Choose Our Baby Due Date Calculator?

• Custom Cycle Calculation: Beyond the standard 40-week model, you can input a custom menstrual cycle length (e.g., 28 or 35 days). The tool will fine-tune your due date accordingly for results that better match your personal physiology.
• Lunar and Weekday Information: Outputs the Gregorian date, Lunar date, and the day of the week simultaneously, catering to families from different cultural backgrounds who value traditional dates and scheduling.
• Dynamic and Intuitive Results: Clearly displays "Days/Weeks Pregnant" and "Days Remaining Until Due Date." The data updates automatically based on the current date, helping you track your pregnancy progress at any time.

How to Use the Tool

1. In the "Last Menstrual Period" field, select or enter the exact date of the first day of your last period.
2. (Optional) In the "Menstrual Cycle" field, enter your average cycle length in days (default is 28 days).
3. Click the "Calculate" button, and the page will instantly display your detailed due date and related timeline information.

Frequently Asked Questions (FAQ)

Is the due date calculation accurate?
The estimated due date is a theoretical calculation based on your LMP and an average pregnancy length of 280 days. The actual delivery date is influenced by many factors, and giving birth anywhere within two weeks before or after your due date is considered completely normal. These results are for reference only and cannot replace clinical diagnosis.

How do I calculate my due date if my periods are irregular?
If your menstrual cycle is irregular or longer than 28 days, it is recommended to use an early ultrasound (between 11-13 weeks) measuring the Crown-Rump Length (CRL) to adjust your due date. This is more accurate than the LMP method. The "Menstrual Cycle" adjustment feature provided by this tool can serve as an initial reference.

Important Notes

Please ensure you enter the accurate first day of your last menstrual period, as this is the foundation of the calculation. The results are for medical reference only and should not be taken as an exact delivery date. For cases involving highly irregular cycles or assisted reproduction (such as IVF), this calculation method may not apply. You should rely on the due date determined by your obstetrician based on ultrasound exams. This tool does not store any of your private data.

Technical Notes & Recommendations

In clinical obstetric practice, calculating the due date is the cornerstone of prenatal care. Naegele's Rule is simple and practical, but it assumes a standard 28-day menstrual cycle with ovulation occurring on day 14. Therefore, for women with cycles other than 28 days, a modified formula can be used: Due Date = LMP + 280 days + (Actual Cycle Length - 28 days). For example, if the LMP is January 1, 2024, and the cycle is 35 days, the estimated due date would be around October 8, 2024 (the standard calculation gives October 7, 2024, plus a 7-day adjustment). An early pregnancy ultrasound (especially CRL measurement between 8-12 weeks) is the gold standard for adjusting the due date, with a margin of error of ±5-7 days. It is highly recommended to complete this scan early in your pregnancy to get the most reliable due date.