Estimate your pregnancy due date and current pregnancy week from the first day of your last menstrual period (LMP). The result is useful for planning, but the date used in prenatal care may be confirmed or revised by a clinician.
Due Date & Pregnancy Week Calculator
Enter the first day of your last period and your usual cycle length.
This is an estimate. ACOG explains that pregnancy dating commonly starts from the first day of the last menstrual period, and first-trimester ultrasound may be used to confirm dating. This tool does not replace prenatal care.
How the due date estimate works
Pregnancy is conventionally dated from the first day of the LMP, even though conception usually occurs later. The American College of Obstetricians and Gynecologists (ACOG) describes the average pregnancy length as about 280 days, or 40 weeks, from the first day of the LMP. A standard LMP calculation assumes a 28-day cycle, so this tool makes a modest calendar adjustment when a different usual cycle length is entered.
Read ACOG’s overview of estimated due dates.
Why a clinician may use a different date
LMP dating can be less reliable when cycles are irregular, the date of the last period is uncertain, ovulation occurred earlier or later than expected, hormonal contraception was recently stopped, breastfeeding has affected cycles, or conception occurred through assisted reproductive technology. ACOG notes that first-trimester ultrasound is the most accurate ultrasound method for establishing or confirming gestational age.
See ACOG’s methods for estimating the due date.
Is the due date the day the baby will be born?
No. An estimated due date is a reference point used to track pregnancy progress; birth can occur before or after that date. It should not be interpreted as a precise prediction of the day labor will begin.
If you conceived through IVF
Assisted-reproduction pregnancies are dated using treatment-specific information such as embryo age and transfer date. Use the date assigned by your fertility or prenatal team rather than a generic LMP calculator.
