What's the difference between gestational age and fetal age?

Gestational age is measured from the first day of your last menstrual period, while fetal age is the actual age of the developing baby (about 2 weeks less than gestational age).

Can I use this calculator if I have irregular periods?

This calculator works best with regular 28-day cycles. For irregular periods, consult with your healthcare provider who may use ultrasound measurements for more accurate dating.

What are the three trimesters of pregnancy?

First trimester: weeks 1-12, Second trimester: weeks 13-26, Third trimester: weeks 27-40. Each trimester has different developmental milestones and care requirements.

Should I rely solely on this calculator for pregnancy planning?

This calculator provides estimates for educational purposes. Always consult with healthcare professionals for prenatal care, confirm pregnancy with medical tests, and follow your doctor's guidance throughout pregnancy.

How does the calculator determine my due date?

The calculator uses Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. This is the standard method used by healthcare providers worldwide.

What are the sources for pregnancy calculations?

Our pregnancy calculations are based on American College of Obstetricians and Gynecologists (ACOG) pregnancy guidelines, World Health Organization (WHO) maternal health standards, and standard gestational age calculation methods.

Pregnancy Calculator

Calculate your due date, current week, trimester, and key milestones instantly. Free pregnancy calculator with multiple methods: LMP, conception date, or ultrasound. Results are estimates only; always confirm with your healthcare provider.

Date Format

Calculation Method *

Last Menstrual Period Date *

Smart Tips

• Pregnancy is typically 40 weeks from the first day of your last menstrual period (LMP)

• Due dates are estimates - only about 5% of babies arrive on their due date

• Ultrasound dating in the first trimester is most accurate for due date calculation

• Each trimester is approximately 13-14 weeks long

• Always confirm due date and prenatal care with your healthcare provider

• Due date is an estimate; most babies are born within two weeks before or after

The Formula

Due Date = Last Menstrual Period + 280 days

LMP = Last Menstrual Period
First day of last period

280 days = Average pregnancy length
40 weeks or 9 months

Trimester = Each trimester is approximately 13-14 weeks
Pregnancy divided into three equal periods

Understanding Pregnancy

First Trimester

Weeks 1-12

Development: Critical

• Major organs and body systems begin to form

• Baby's heartbeat starts around week 6

• Morning sickness and fatigue are common

• First prenatal visit typically scheduled

Second Trimester

Weeks 13-26

Development: Rapid Growth

• Baby's movements become noticeable

• Gender can often be determined via ultrasound

• Energy levels typically improve

• Anatomy scan usually performed around week 20

Third Trimester

Weeks 27-40

Development: Final Preparation

• Baby gains weight and develops fully

• Frequent prenatal visits increase

• Braxton Hicks contractions may occur

• Body prepares for labor and delivery

Key Insights

Due Date Accuracy

Only about 5% of babies are born on their exact due date. Most births occur within 2 weeks before or after the calculated due date.

Calculation Methods

LMP method is most common, but ultrasound dating is more accurate, especially if your cycle is irregular or conception date is uncertain.

Trimester Milestones

Each trimester (12-13 weeks) brings unique developmental milestones and care requirements. Regular prenatal visits are essential.

Prenatal Care

Early and regular prenatal care is crucial for monitoring both maternal and fetal health throughout pregnancy.

Medical Disclaimer

Important: This pregnancy calculator is for educational and informational purposes only. It provides estimates based on standard pregnancy calculations and should not be used as a substitute for professional medical advice, diagnosis, or treatment.

Consult Healthcare Providers: Always consult with qualified healthcare professionals for personalized medical advice regarding pregnancy, prenatal care, and reproductive health. This calculator cannot replace professional medical guidance.

Individual Variations: Every pregnancy is unique. These calculations are estimates and may not accurately reflect your specific pregnancy timeline. Individual factors such as health conditions, medications, and lifestyle can significantly affect pregnancy.

Frequently Asked Questions

Due date calculations are estimates based on a 40-week (280-day) pregnancy from the first day of the last menstrual period. Only about 5% of babies are born on their exact due date; most arrive within a window of about two weeks before to two weeks after. Early ultrasound (first trimester) can refine the estimate. Your healthcare provider will use the due date to schedule tests and monitor growth, but it is always a reference date, not a guarantee.

Gestational age is measured from the first day of your last menstrual period (LMP) and is the standard used by most providers and this calculator. Fetal (or embryonic) age is the actual time since conception and is about two weeks less than gestational age, because ovulation and fertilization typically occur around two weeks after the LMP. When a provider says "12 weeks pregnant," they usually mean 12 weeks gestational age; the fetus is about 10 weeks old by fetal age.

This calculator assumes a typical 28-day cycle and ovulation around day 14. If your cycles are irregular, longer, or shorter, the LMP-based due date may be less accurate. In that case, your healthcare provider often uses an early ultrasound (especially in the first trimester) to measure the fetus and assign a due date. Always confirm dating and prenatal care with your doctor or midwife, who can account for your individual cycle and history.

The first trimester is weeks 1-12 from the LMP: early development, first heartbeat, and most early prenatal visits and screening. The second trimester is weeks 13-26: organ development, movement often felt, anatomy scan. The third trimester is weeks 27-40: growth and lung maturation, and preparation for birth. Each trimester has different milestones, screening options, and care guidelines, so regular prenatal visits are important throughout.

No. This calculator gives an estimated due date for general information only. It is not a substitute for medical care. You should confirm pregnancy with a healthcare provider, get prenatal care, and follow your doctor's or midwife's guidance for dating, screening, and delivery planning. Use this tool to get a rough idea of your due date and trimester; your provider may adjust the date based on your history and, if needed, early ultrasound.

The calculator uses Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). That assumes a 28-day cycle with ovulation around day 14. Some versions subtract 3 months and add 7 days from the LMP to get the same result. This rule is the standard starting point used by obstetricians and midwives; early ultrasound may be used to adjust the date if the LMP is uncertain or cycles are irregular.

Our pregnancy calculations follow the same Naegele's rule and 40-week gestational model used in clinical practice and referenced in guidelines from the American College of Obstetricians and Gynecologists (ACOG) and the World Health Organization (WHO). Gestational age from LMP and trimester definitions are consistent with standard obstetric and maternal health resources. This tool is for educational use only; clinical decisions should be made with your healthcare provider.

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Note:Pregnancy timeline calculations are estimates based on standard gestational age formulas. Actual pregnancy progression may vary. Always consult with healthcare professionals.