Gestational Age Calculator
HealthCalculate gestational age in weeks and days, plus trimester, from the number of days since your last menstrual period (LMP).
Gestational Age (Weeks)
20
Additional Days
0
Trimester
2
What is a Gestational Age?
The Gestational Age Calculator computes gestational age in weeks and days, along with trimester, from the number of days since your last menstrual period (LMP) — the standard medical method for dating pregnancy.
For a related pregnancy dating tool, see the Pregnancy Due Date Calculator and Fundal Height Calculator.
How to use this Gestational Age calculator
- Enter the number of days since your last menstrual period (LMP).
- Read the Gestational Age, Additional Days, and Trimester instantly.
Formula & Methodology
Gestational Weeks = ⌊Days Since LMP ÷ 7⌋ Additional Days = Days Since LMP mod 7 Trimester: 1st (weeks 0-12), 2nd (weeks 13-27), 3rd (weeks 28+) Worked example — 140 days since LMP: Gestational Weeks = ⌊140 ÷ 7⌋ = 20 weeks Additional Days = 140 mod 7 = 0 days Trimester = 2nd
Frequently Asked Questions
Gestational age is the standard way pregnancy duration is measured, counted in weeks and days starting from the first day of the last menstrual period (LMP), rather than from the actual date of conception.
The exact date of conception is often unknown or difficult to pinpoint, while the first day of the last menstrual period is generally a known, consistent reference point, which is why LMP became the medical standard for dating pregnancy.
The calculator divides the total days since LMP by 7 to get whole weeks, with the remainder showing the additional days into the current week.
This calculator uses commonly cited trimester boundaries: the first trimester runs through week 12, the second trimester from week 13 through 27, and the third trimester from week 28 onward.
No — gestational age (counted from LMP) is typically about two weeks ahead of fetal age (counted from actual conception), since ovulation and conception usually occur roughly two weeks after the start of the last period.
The [Fundal Height Calculator](/fundal-height-calculator/) estimates gestational age from a physical measurement taken during a prenatal visit, offering an alternative (though less precise) reference point compared to LMP-based dating.
Ultrasound dating, especially in early pregnancy, measures fetal size directly and can sometimes differ slightly from LMP-based calculations if ovulation didn't occur exactly on the typical cycle day assumed by LMP dating.
The [Pregnancy Due Date Calculator](/pregnancy-due-date-calculator/) projects forward to estimate a due date from LMP, while this calculator shows the current gestational age at any point during the pregnancy.
If your LMP date is uncertain, an ultrasound dating scan (particularly one done in the first trimester) generally provides a more reliable estimate of gestational age than LMP-based calculation alone.
Full term is generally considered to span 39 to 40 weeks of gestational age, though babies born anywhere from 37 to 42 weeks are typically categorized within the broader term range.
Also known as