Pregnancy Due Date Calculator
Our pregnancy calculator helps you estimate your due date and track your pregnancy journey week by week. By entering the first day of your last menstrual period or your conception date, you get a personalized timeline that shows exactly where you are in your pregnancy, which trimester you are in, and how many weeks and days until your expected delivery. Pregnancy is traditionally measured as 40 weeks from the first day of the last menstrual period, even though actual fetal development begins about two weeks later at ovulation. Understanding your pregnancy timeline helps you and your healthcare provider schedule important prenatal visits, screenings, and tests at the right gestational ages. Whether you are just confirming a pregnancy or well into your second trimester, having a clear week-by-week overview gives you peace of mind and helps you prepare physically and emotionally for what lies ahead. Our calculator also shows key milestone dates like when your baby's major organs form, when you might first feel movement, and when viability typically occurs around 24 weeks. Having these reference points makes the abstract concept of pregnancy feel more concrete and manageable.
What Is
A pregnancy calculator is a tool that estimates your expected delivery date (EDD) and maps out the entire 40-week gestational timeline. The most widely used method for calculating due dates is Naegele's Rule, which adds 280 days (40 weeks) to the first day of your last menstrual period (LMP). This rule assumes a regular 28-day menstrual cycle with ovulation occurring on day 14. The formula works as follows: EDD = LMP date + 1 year - 3 months + 7 days. For example, if your LMP started on January 1, your estimated due date would be October 8 of the same year. However, only about 5% of babies are born exactly on their due date -- most arrive within a two-week window before or after. Modern pregnancy calculators can also work backward from an ultrasound measurement or forward from a known conception date if you tracked ovulation. The calculator divides your pregnancy into three trimesters: the first trimester (weeks 1-13) when major organs and structures form, the second trimester (weeks 14-27) when the baby grows rapidly and movement becomes noticeable, and the third trimester (weeks 28-40) when the baby gains weight and matures in preparation for birth. Each trimester has specific developmental milestones, recommended prenatal tests, and nutritional needs. The calculator also estimates important dates like the end of the embryonic period (week 10), when the risk of miscarriage drops significantly, and the age of viability (around week 24), when a baby has a chance of survival outside the womb with intensive medical support. Beyond the due date, the calculator shows you your current gestational age, which your doctor uses to track fetal growth and plan care.
How to Use
- Enter the first day of your last menstrual period in the date field. This is the most common starting point used by healthcare providers to estimate your pregnancy timeline and due date.
- Alternatively, if you know your exact conception date from ovulation tracking or fertility treatments, select the conception date option for a more precise calculation.
- Click the calculate button to generate your complete pregnancy timeline, which includes your estimated due date, current week and day of pregnancy, and active trimester.
- Review the milestone markers that show when key developmental events occur, such as heartbeat appearance around week 6 and first movements around week 18 to 22 for first-time mothers.
- Share the results with your healthcare provider at your first prenatal visit. They may adjust your due date based on early ultrasound measurements in the first trimester.
- Check back regularly to see your progress update automatically -- the calculator tracks your advancing pregnancy week by week as time passes.
Examples
Input: Weight: 68 kg, Height: 170 cm
Process: BMI=68/(1.7)²=23.5
Result: BMI=23.5 → Normal
Input: Male: 68kg, 170cm, 30yo
Process: BMR=1598 kcal/day
Result: BMR=1598 kcal/day (resting metabolism)
Input: Weight: 55 kg, Height: 160 cm
Process: BMI=55/(1.6)²=21.5
Result: BMI=21.5 → Normal
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Frequently Asked Questions
How accurate is the due date from this calculator?
The estimated due date is a useful reference point but not an exact prediction. Only about 5% of babies are born precisely on their calculated due date. Most healthy pregnancies deliver within a two-week window before or after the estimated date, which doctors consider a normal range. If your cycle length differs significantly from the standard 28 days or if your ovulation timing was irregular, the due date may be less accurate. Early ultrasounds performed between 8 and 13 weeks provide the most reliable dating, with an accuracy of plus or minus about 5 to 7 days. Your healthcare provider may adjust your due date based on these ultrasound measurements if they differ from the LMP-based calculation by more than a specified threshold.
How is the due date calculated from the last menstrual period?
The standard method is called Naegele's Rule: take the first day of your last menstrual period, add one year, subtract three months, and add seven days. This adds 280 days total and assumes a 28-day cycle with ovulation on day 14. For example, an LMP of March 15 gives a due date of December 22. However, this method has limitations. If your cycles are shorter than 26 days or longer than 32 days, or if your ovulation regularly occurs on a different day than day 14, the calculation may be off by several days. In such cases, an early ultrasound measurement of your baby's size provides a more accurate gestational age and your provider will likely use that date instead.
What if I do not know my last menstrual period date?
If you cannot recall your LMP or if your periods are irregular, an early ultrasound is the best way to determine your gestational age and due date. During the first trimester, specifically between 8 and 13 weeks of gestation, ultrasound measurements of the crown-rump length can estimate gestational age with an accuracy of within 5 to 7 days. Your healthcare provider will use this measurement to establish an official due date. If you had fertility treatments such as IVF or IUI, the conception date is known precisely and can be used directly by adding 23 days for fertilization age or 38 weeks from the date of fertilization.
Can the calculator determine the baby's father or conception date?
No, a pregnancy calculator cannot determine paternity or the exact date of conception. It can only estimate timelines backward from a known LMP or forward from a known conception date that you provide. Paternity can only be determined through DNA testing, either during pregnancy through non-invasive prenatal testing or after birth. If you are unsure of the conception date, the window of fertility typically spans about 5 to 6 days per cycle because sperm can survive in the reproductive tract for up to 5 days while the egg is viable for only 12 to 24 hours after ovulation.
When should I see a doctor after using this calculator?
You should schedule your first prenatal visit as soon as you confirm your pregnancy, ideally within the first 6 to 8 weeks of gestation. At this appointment, your healthcare provider will confirm the pregnancy with an ultrasound, establish an official due date, take a complete medical history, and order initial blood work to check for blood type, immunity to certain infections, and baseline health markers. Early prenatal care is important because it allows your provider to identify any risk factors, start you on prenatal vitamins with folic acid if you have not already begun, and give you guidance on nutrition, exercise, and lifestyle adjustments.