Estimate your due date based on the first day of your last menstrual period.
The Pregnancy Due Date calculator is a valuable tool for expecting parents to estimate the arrival of their new family member. Based on the widely recognized Naegele's rule, this calculator uses the date of your last menstrual period (LMP) and your average cycle length to determine an Estimated Date of Delivery (EDD). Understanding your timeline helps in planning prenatal care milestones, monitoring fetal development, and preparing for the physical changes ahead.
This calculator is intended for individuals who have a regular menstrual cycle and know the first day of their last period. While it provides a highly useful estimate, it is important to note that very few babies arrive exactly on their due date—most are born within a two-week window on either side. This tool provides educational information to support your journey but does not replace the dating ultrasound or clinical assessment performed by an obstetrician or midwife. Always consult your healthcare professional to confirm your gestational age and delivery timeline.
Type in your own measurements — the grey hints are just examples.
Leave at 28 if you are unsure.
To get your estimated due date, you will need to enter two pieces of information. First, select the date of the 'First Day of your Last Menstrual Period' from the calendar picker. This is the date when your last period actually began, not when it ended. Second, enter your 'Average Cycle Length' in days. The default is 28 days, which is the standard average, but you can adjust this between 20 and 45 days if your cycle is typically shorter or longer. If you are unsure of your cycle length, leaving it at 28 days will provide a standard estimate. The calculator will then display your EDD, your current gestational age in weeks and days, and the number of days remaining until your estimated arrival.
The primary result is your Estimated Date of Delivery (EDD), which marks the 40-week point of a typical pregnancy. The tool also provides your current 'gestational age,' which is the standard clinical way to track how far along you are. If the result indicates you are 'past your estimated due date,' it simply suggests you have reached the 40-week mark; it is common for first-time pregnancies or certain physiological conditions to extend slightly beyond this date.
It is crucial to recognize the limitations of this calculation. The formula assumes a standard ovulation window (typically 14 days after the start of the period), which can vary significantly between individuals. If you have irregular cycles, were breastfeeding, or conceived shortly after stopping hormonal contraception, the LMP-based date may be significantly less accurate. Furthermore, the calculator does not account for pregnancies involving multiples (twins or triplets), which often involve different physiological milestones and typically have earlier delivery timelines.
Accuracy is also affected by how precisely you recall the first day of your last period. Even with perfect recall, many factors influence the actual date of birth. Environmental factors, maternal health history, and fetal development rates all play a role. A clinical dating ultrasound, typically performed in the first trimester, is generally considered the most accurate way to establish a due date because it measures the physical size of the embryo or fetus, which varies less than menstrual cycles in early development.
Use this information as a guide for your early planning and to help schedule your initial appointments. We strongly recommend discussing the results with your midwife or obstetrician during your first prenatal visit. They will consider your full medical history, including previous pregnancies and any underlying conditions, to ensure the most accurate tracking of your pregnancy's progress and to help you understand the signs of labor to watch for as you approach your delivery window.
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A pregnancy due date — also called the estimated date of delivery (EDD) — is most commonly calculated by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). This approach, known as Naegele's rule, is the standard method used in clinical practice when the LMP is reliably known and cycles are approximately 28 days.
The estimated due date represents the midpoint of a normal term range. Only around 5% of babies are born on their exact due date. A full-term pregnancy is considered to span from 39 to 40 weeks and 6 days, while early term runs from 37 to 38 weeks. Knowing your EDD helps guide routine antenatal checks, screening timing, and delivery planning.
Due dates calculated from LMP assume a regular 28-day cycle and may be inaccurate for those with irregular periods. Early ultrasound — typically performed between 8 and 13 weeks — is more accurate for dating and will take precedence over LMP-based estimates if there is a discrepancy. This calculator is for general reference only.
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Any concerns during pregnancy — including unusual symptoms, reduced fetal movement, or bleeding — should be assessed by a midwife or obstetrician without delay.
Sources & Methodology
These references support the formula, educational ranges, and interpretation used in this calculator. Results are estimates and are not a diagnosis.
Medical Disclaimer
This calculator and its accompanying content are provided for general educational and informational purposes only. They are not intended to be, and should not be used as, a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider with any questions you may have regarding a medical condition or before making decisions about your health. Never disregard professional medical advice or delay seeking it because of information provided by this tool. Healio360 does not warrant the accuracy, completeness, or usefulness of this content and assumes no liability for actions taken based on it.