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Gestational Age Calculator

Find your current pregnancy weeks and days from your last menstrual period.

How it is calculated

You enter the number of days that have passed since the first day of your last menstrual period (day 0 is that first day). The tool converts the days to weeks and days with whole-number division: weeks = ⌊days ÷ 7⌋ and extra days = days mod 7. The result is shown in the obstetric style weeks+days, so 14+2 means 14 completed weeks and 2 days. A second line gives the completed weeks on their own.

Any decimal part of the day count is dropped. The tool accepts values from 0 up to 330 days and returns nothing outside that range. It counts from the LMP date, not from conception, so it assumes a typical cycle; if your cycles are irregular, or an early ultrasound gave a different dating, your care provider's figure takes precedence. It does not work out a due date and is not medical advice.

Worked example

Say 100 days have passed since the first day of the last period. Dividing by 7 gives 14 with a remainder: 14 × 7 = 98, and 100 − 98 = 2. The gestational age is therefore 14+2, meaning 14 weeks and 2 days, and the completed weeks figure is 14. Exactly 280 days would show 40+0, the usual full-term mark counted from the LMP, and 7 days later it would show 41+0.

Try this example →

Common mistakes

  • Counting from the estimated conception date. Gestational age starts at the first day of the last period, about two weeks earlier, so the number would be too low.
  • Using the last day of the period, or the date the test turned positive, as day 0.
  • Reading 14+2 as 14.2 weeks. It is 14 weeks and 2 days, not a decimal fraction of a week.
  • Typing a number of weeks into the days field. Twenty weeks is 140 days; entering 20 shows 2+6.
  • Entering more than 330 days or a negative number, which gives no result.

Sources

About this calculator

Gestational age is the standard way pregnancy duration is measured in obstetrics, counted in completed weeks and days from the first day of the last menstrual period (LMP) rather than from the estimated date of conception, which typically falls about two weeks later. A full-term pregnancy runs roughly 40 weeks (280 days) from LMP, and this convention is used consistently across prenatal visits, ultrasound dating and due-date calculations even though actual ovulation and fertilization occur later in the cycle.

Obstetricians, midwives and pregnant people use gestational age to track fetal development milestones, schedule prenatal screenings and tests that are only meaningful within specific week windows, and determine the estimated due date, with early ultrasound measurements sometimes used to adjust the LMP-based estimate if cycle length was irregular.

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