Calculate your estimated due date, conception date, and current pregnancy week based on your last menstrual period. Track your pregnancy journey with detailed trimester information.
Pregnancy duration is typically calculated from the first day of your last menstrual period (LMP), not from the actual conception date. This method is used because the LMP date is usually known, while the exact conception date is often uncertain.
The most common method adds 280 days (40 weeks) to the first day of your LMP. This assumes a regular 28-day menstrual cycle with ovulation occurring on day 14. The calculation follows Naegele's Rule: LMP date + 7 days - 3 months + 1 year.
If you know the exact conception date, 266 days (38 weeks) are added to calculate the due date. This method is more accurate when conception timing is precisely known, such as with assisted reproductive technologies.
First-trimester ultrasounds (especially between 8-13 weeks) are considered the most accurate method for establishing gestational age, with accuracy within 3-5 days. Your healthcare provider may adjust your due date based on ultrasound measurements.
Pregnancy is divided into three trimesters, each lasting approximately 13-14 weeks. Each trimester brings unique developmental milestones and physical changes:
The first trimester is a period of rapid development. Major organs and body systems begin to form.
Often called the "golden period" of pregnancy, many women feel their best during this time.
The final stretch as baby prepares for birth and gains most of their weight.
Understanding key milestones throughout pregnancy helps you know what to expect at each stage:
Most home pregnancy tests can detect pregnancy around the time of your missed period. The embryo is about the size of a sesame seed.
Your first prenatal appointment typically occurs around this time. You may have your first ultrasound and hear the heartbeat.
Miscarriage risk drops significantly. Many women choose to announce their pregnancy after this milestone. Baby is about 2.5 inches long.
A detailed ultrasound checks baby's development and can reveal the sex. You're likely feeling regular movements now.
Babies born at 24 weeks have a chance of survival with intensive medical care, though significant risks remain. Baby weighs about 1.3 pounds.
Prenatal visits become more frequent. Baby's eyes can open and close, and they're developing sleep-wake cycles.
Baby is considered full term and ready for birth. Lungs are mature enough to function outside the womb. Average weight is 6-7 pounds.
Your estimated due date arrives! Only about 4-5% of babies are born on their exact due date. Most are born within 2 weeks before or after.
The age of the pregnancy calculated from the first day of your last menstrual period. This is the standard measurement used by healthcare providers and is typically 2 weeks longer than fetal age (calculated from conception).
The predicted date when your baby will be born, calculated as 40 weeks from your LMP. Remember, this is an estimate - babies can safely arrive anywhere from 37 to 42 weeks.
Pregnancies are categorized by when baby is born:
Several factors can influence when your baby actually arrives:
If your cycles are longer or shorter than 28 days, or irregular, the standard calculation may be less accurate. Your healthcare provider may adjust your due date based on early ultrasound measurements.
First-time mothers are slightly more likely to deliver after their due date, while women who have given birth before may deliver earlier. However, this varies greatly between individuals.
Twins and higher-order multiples typically arrive earlier than singletons. The average twin pregnancy lasts 35-36 weeks, while triplets average 32-33 weeks.
Maternal age, overall health, and pregnancy complications can influence delivery timing. Your healthcare provider will monitor these factors throughout your pregnancy.
Contact your healthcare provider immediately if you experience:
The calculator provides an estimate based on standard pregnancy duration. Only about 4-5% of babies are born on their exact due date. Most babies arrive within 2 weeks before or after the estimated due date. First-trimester ultrasounds provide the most accurate dating.
If you're unsure of your LMP date, your healthcare provider can estimate your due date using an early ultrasound, which measures the size of the embryo or fetus. This is most accurate when done between 8-13 weeks of pregnancy.
Yes, your healthcare provider may adjust your due date based on early ultrasound measurements, especially if there's a significant difference (more than 5-7 days) between the ultrasound dating and LMP-based calculation. Due dates are typically only changed in the first trimester.
Going past your due date is common and usually not a concern. Most providers will monitor you more closely after 40 weeks and may discuss induction between 41-42 weeks to reduce risks associated with post-term pregnancy.
Healthcare providers count pregnancy in weeks because it's more precise. A full-term pregnancy is 40 weeks, which is approximately 9 months and 1 week (not 9 months exactly). This is why pregnancy is often described as lasting "9 months" even though it's actually closer to 10 months.
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