Enter the first day of your last period to see your gestational age in weeks and days, your due date, and where that lands on the ACOG term scale.
Estimate only.
There are two clocks running on any pregnancy. Gestational age counts from the first day of your last menstrual period, the standard used by this calculator and by obstetric care generally. Fetal age counts from conception itself, which lands roughly two weeks later. Under the gestational age convention, a person is considered about two weeks pregnant at the moment of ovulation, before an egg has even been fertilized. Both numbers describe the same pregnancy; they simply start the clock at a different point.
Once gestational age reaches the late 30s in weeks, providers stop talking in weeks alone and start using a small set of named categories set by the American College of Obstetricians and Gynecologists. This calculator reports which one your current gestational age falls into.
| Category | Gestational age |
|---|---|
| Preterm | Before 37 weeks |
| Early term | 37 weeks 0 days to 38 weeks 6 days |
| Full term | 39 weeks 0 days to 40 weeks 6 days |
| Late term | 41 weeks 0 days to 41 weeks 6 days |
| Post term | 42 weeks and beyond |
LMP based dating is a starting point, not the final word. An early ultrasound, ideally between about 8 and 13 weeks, measures the fetal crown rump length and can date a pregnancy independently of your reported last period. When the two disagree by more than a few days, providers typically defer to the ultrasound, particularly if your cycles are irregular or you are unsure of your last period date. This calculator only knows what you enter, so treat its output as a working estimate to compare against your chart, not a replacement for it.
Use "Copy shareable link" to generate a page address that carries your last period date with it, handy for sending to a partner or pasting into your own notes. "Print summary" strips away the navigation and footer and leaves a clean printable page with just the results, useful for a prenatal folder or an appointment where you want the numbers on paper rather than a phone screen.
Estimate only, not medical advice. Generated by pregnancy-tools.com
Gestational age counts from the first day of your last period. Fetal age counts from conception, about two weeks later, so a person is considered two weeks pregnant at ovulation before fertilization has even occurred.
Conception date is rarely known precisely, while the first day of a last period usually is. Clinicians standardized on LMP so dating stays consistent even when the exact conception day is unknown.
Following ACOG categories: preterm is before 37 weeks, early term is 37 weeks 0 days to 38 weeks 6 days, full term is 39 weeks 0 days to 40 weeks 6 days, late term is 41 weeks 0 days to 41 weeks 6 days, and post term is 42 weeks and beyond.
Yes. A dating scan between about 8 and 13 weeks, measuring crown rump length, can adjust the estimate if it differs meaningfully from the LMP based date.