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Tiếng ViệtPregnancy week and
due date calculator
Enter your last period or your ultrasound details to see how far along you are, your estimated due date and how big your baby is this week.
Enter a date to see your result here.
Length and weight are the average estimate for that week; your baby's measurements may differ. Sources
How is it calculated?
From your last period: Pregnancy is counted from the first day of your last period. The estimated due date is 280 days (40 weeks) after that date; if your cycle is longer or shorter than 28 days, it moves forward or back by the difference.1,2
From an ultrasound: The count runs backwards and forwards from the gestational age measured on the ultrasound. An ultrasound in the first trimester is considered the most reliable way to date a pregnancy.1,3
This is an estimate. The date set by your doctor is the one to go by.
Sources
- ACOG Committee Opinion No. 700: Methods for Estimating the Due Date (2017, reaffirmed 2025)
- NHS: Pregnancy due date calculator
- NICE NG201: Antenatal care – Recommendations
Baby's length and weight
- Stirnemann J et al.: International estimated fetal weight standards of the INTERGROWTH-21st Project (Ultrasound Obstet Gynecol 2017)
- Kiserud T et al.: The World Health Organization Fetal Growth Charts: A Multinational Longitudinal Study of Ultrasound Biometric Measurements and Estimated Fetal Weight (PLoS Med 2017)
- INTERGROWTH-21st: Newborn Size – international standards for newborn weight, length and head circumference (Villar J et al., Lancet 2014)
- INTERGROWTH-21st: International Newborn Size References for Very Preterm Infants – Length, boys (Villar J et al., Lancet 2016)
- Papageorghiou AT et al.: International standards for early fetal size and pregnancy dating based on ultrasound measurement of crown–rump length in the first trimester of pregnancy (Ultrasound Obstet Gynecol 2014)
- Robinson HP, Fleming JE: A critical evaluation of sonar "crown-rump length" measurements (Br J Obstet Gynaecol 1975)
Frequently asked questions
Why is pregnancy counted from the last period?
The day of conception usually isn't known, while the first day of the last period usually is. So pregnancy is counted from about two weeks before conception.1
What does "24 weeks 3 days" mean?
It means you have completed 24 weeks and are on day 3 of week 25. Doctors write gestational age this way, as completed weeks and days.
What if my cycle is irregular?
With irregular cycles, a calculation from the last period is less reliable. In that case, calculating from an ultrasound measurement gives a more accurate result.1