Gestation Week from EDD Calculator
Pregnancy is dated as a 280-day (40-week) term counted from the first day of the last menstrual period. The estimated due date (EDD) marks day 280. To find the gestational age on any given day, you count backward from the EDD: the weeks and days of pregnancy equal the total term minus the days still remaining. This calculator takes your due date and a reference date (today by default), works out the days until the EDD, and reports the gestational age in completed weeks plus extra days. Adjust the term length if your provider uses a different dating basis.
Gestational age formula
Days remaining = EDD - reference date
Total gestation days = term length - days remaining
Weeks = floor(total gestation days / 7)
Extra days = total gestation days mod 7
The default term is 280 days (40 weeks), the Naegele convention from the last menstrual period. Gestational age is read as weeks plus days, for example 32+4 means 32 completed weeks and 4 days.
Pregnancy dating context
- The 40-week (280-day) term is measured from the first day of the last menstrual period, not from conception.
- Conception-based dating is roughly 266 days (38 weeks), about two weeks shorter than LMP dating.
- Term birth is commonly defined as 39 weeks 0 days through 40 weeks 6 days; preterm is before 37 weeks.
- Ultrasound dating can revise the EDD, which shifts every gestational-age figure derived from it.
- This tool performs date arithmetic only; clinical dating decisions belong to your healthcare provider.
Gestation week from EDD: frequently asked questions
How is gestational age calculated from the due date?
Standard obstetric dating uses a 280-day (40-week) pregnancy from the first day of the last menstrual period (LMP). Because the estimated due date (EDD) is LMP plus 280 days, the gestational age on any date equals 280 days minus the number of days remaining until the EDD. This calculator subtracts the days remaining from 280, then expresses the result as completed weeks plus extra days.
What is the difference between weeks and weeks plus days?
Gestational age is reported as completed weeks and days, for example 32 weeks and 4 days (written 32+4). The week number counts completed weeks since the LMP, and the day number is the remainder (0 to 6). A baby is considered full term from 39 weeks 0 days through 40 weeks 6 days per common clinical definitions.
Does this use a 40-week term?
Yes. The default is 280 days, which is 40 weeks, the convention based on Naegele's rule. You can edit the total term length if your clinician uses a different basis, such as dating from conception (which is about 266 days, or 38 weeks).
Is this a substitute for medical advice?
No. This is an arithmetic tool for converting between an EDD and gestational age. Pregnancy dating is confirmed and may be adjusted by a clinician using ultrasound and clinical assessment. Always rely on your healthcare provider for dating decisions.
What if today is after the due date?
If the chosen date is on or after the EDD, the gestational age is 40 weeks or more. The calculator will continue counting past 280 days, so a date 3 days after the EDD shows 40 weeks and 3 days (40+3), which is post-term territory.
Official sources
- U.S. Centers for Disease Control and Prevention: CDC reproductive and maternal health.
- National Institutes of Health: Eunice Kennedy Shriver National Institute of Child Health and Human Development.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.