Pregnancy Calculator
Find out how many weeks pregnant you are and your trimester.
Pregnancy dates are estimates and do not replace prenatal medical care.
Pregnancy calculator
Choose a calculation method and enter the date details you know.
LMP method counts pregnancy from the first day of the last period.
Cycle length can shift estimated ovulation and due date. Accepted range: 21–45 days; leaving it blank uses 28 days.
Pregnancy dates are estimates. Prenatal care, ultrasound dating, IVF details, and complex medical histories should be guided by qualified healthcare professionals.
Gestational age explained
Due date and trimester guide
First trimester
Weeks 1–13
Early pregnancy dating is commonly based on gestational age from LMP.
Second trimester
Weeks 14–27
Prenatal care timing and scans should follow clinician guidance.
Third trimester
Weeks 28–40+
The final trimester includes continued growth, monitoring, and birth preparation.
Due date is an estimated delivery date, not a guaranteed birth date. Most babies are not born exactly on the due date, and trimester boundaries can vary slightly by source.
Calculation methods explained
Last menstrual period
Uses the first day of your last period and cycle length.
Conception date
Uses a known or estimated conception date.
Due date
Works backward from an existing estimated due date.
IVF transfer
Uses transfer date and embryo age.
Why dates can change
Exact delivery date cannot be predicted by a calculator. Calculated pregnancy week is a planning estimate, not a diagnosis.
Limitations and medical disclaimer
Calculator results are informational only. Pregnancy dating is approximate, and prenatal care should be guided by healthcare professionals.
IVF details and complex medical histories should be reviewed clinically.
Seek urgent medical attention for symptoms such as heavy bleeding, severe abdominal pain, fainting, severe headache, chest pain, shortness of breath, or reduced fetal movement later in pregnancy.
Formula / date explanation
LMP method: Estimated Due Date = LMP + 280 days + (Cycle Length − 28 days)Conception method: Estimated Due Date = Conception Date + 266 daysDue date method: Estimated Pregnancy Start = Due Date − 280 daysIVF method: Estimated Due Date = Transfer Date + 266 days − Embryo Age (days)Gestational Age = Today − Estimated Pregnancy StartPregnancy Progress = Gestational Age Days ÷ 280 × 100280 days is about 40 weeks from LMP. With a 28-day cycle the cycle adjustment is 0 days; a 35-day cycle adds 7 days and a 21-day cycle subtracts 7 days. 266 days is about 38 weeks from conception. For IVF, a 5-day embryo transfer gives transfer date + 261 days and a 3-day embryo transfer gives transfer date + 263 days. Ultrasound or clinician assessment may override calculator estimates.
Sources: ACOG: Methods for Estimating the Due Date and NHS: Pregnancy due date calculator.
Frequently Asked Questions
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Estimate only. This calculator is for general education and planning. It is not medical advice, and not medical, nutrition, fitness, diagnosis, treatment, or emergency advice. Personal factors can change results. Dates are estimates based on the inputs provided. Cycle length, ovulation timing, pregnancy dating, and medical factors can vary. Speak with a qualified professional for personal guidance.
Related reading
Learn the formula, assumptions, examples, or context behind this tool.