Due Date Calculator

About the Due Date Calculator

The Due Date Calculator estimates your estimated due date (EDD) and current pregnancy week from the first day of your last menstrual period (LMP). It is based on the standard obstetric rule that pregnancy lasts about 40 weeks (280 days) from the LMP. You can optionally enter your average cycle length for a more personalized estimate. The result is for planning and reference only; your healthcare provider may adjust the date using ultrasound or clinical assessment.

How to Use

Enter the first day of your last menstrual period. If your cycle is not 28 days, enter your average cycle length when the tool offers that option. The calculator will show your estimated due date and how many weeks you are. Use this information to plan appointments, work, and family arrangements. If you are unsure of your LMP or have irregular cycles, an early ultrasound can help establish or correct your due date.

• Select the date of your last menstrual period (LMP).
• Enter your average cycle length if the tool supports it (default is often 28 days).
• Review the calculated due date and current pregnancy progress.

How to Use This Due Date Calculator

Enter the first day of your last menstrual period (LMP). The Due Date Calculator estimates your expected due date (EDD)—typically 280 days (40 weeks) from the LMP—and may show trimester and current week. Some tools also allow entry based on conception date or IVF transfer date. The result is an estimate; your provider may adjust it with early ultrasound. Use it for planning and general awareness; always follow your doctor or midwife for official due date and prenatal care.

Naegele's Rule

Many due date calculators use a method derived from Naegele's rule: add seven days to the first day of the LMP, then subtract three months. That gives a date 280 days (40 weeks) from the LMP. The rule assumes a 28-day cycle and ovulation around day 14. If your cycle is longer or shorter, or if you ovulate earlier or later, the true due date may differ. Early ultrasound (first trimester) is often used to refine the EDD when needed.

Accuracy of Due Dates

Only a small percentage of babies are born exactly on the calculated due date. Most are born within about two weeks before or after. Preterm birth (before 37 weeks) and post-term pregnancy (after 42 weeks) are possible and may require extra monitoring. This calculator does not replace clinical care. Always follow the guidance of your doctor or midwife for due date, screenings, and delivery planning.

How the Due Date Is Computed

The calculator applies Naegele's rule: take the first day of the last menstrual period (LMP), add 7 days, then subtract 3 months. That yields a date 280 days (40 weeks) from the LMP. The rule assumes a 28-day cycle and ovulation around day 14. Some tools allow entry of average cycle length to adjust; a 30-day cycle may shift the estimate by a few days. Early ultrasound (first trimester) can refine the EDD when the LMP is uncertain or cycles are irregular. Conception-based or IVF-based calculators use different formulas; this tool focuses on LMP-based estimation.

Limitations

This calculator assumes a standard 40-week pregnancy from the LMP. Irregular cycles, late ovulation, or uncertainty about the LMP can affect accuracy. It does not account for multiples, medical conditions, or provider-specific protocols. For official due date and prenatal care, always follow your doctor or midwife. This tool is for planning and reference only.

When to Use and Tips

Use the Due Date Calculator when you know the first day of your last menstrual period (LMP) and want an estimated due date (EDD) for planning, appointments, or curiosity. If your cycle is longer or shorter than 28 days, some tools let you adjust; otherwise the result is based on the standard rule. Early ultrasound (first trimester) can refine the EDD when the LMP is unclear. Do not use this tool as the sole basis for medical decisions; your provider may assign a different date after examination or ultrasound. This tool is for informational use only.

How the Due Date Is Computed

The standard method adds 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is irregular the estimate may be less accurate. Your provider may adjust the date after an early ultrasound. This tool is for informational use only.

Limitations

LMP-based estimates assume a 28-day cycle and ovulation around day 14. IVF and IUI often use transfer or retrieval dates. For official due date and prenatal care, always follow your doctor or midwife. This tool is for informational use only.

Limitations

LMP-based estimates assume a 28-day cycle. IVF and IUI often use transfer or retrieval dates. For official due date follow your doctor or midwife. This tool is for informational use only.

Disclaimer

This tool is for informational use only. It does not provide medical advice. Pregnancy and due date should be confirmed and managed by a qualified healthcare professional. For any questions about your dates or pregnancy health, consult your doctor or midwife.