Gestational age calculator
Gestational age is the weeks-and-days number on your chart — usually from LMP (or an IVF LMP-equivalent), not the afternoon you think you conceived. Enter LMP, EDD, or transfer details and get X weeks Y days. Estimate only — not medical advice.
Enter a date to see an estimate.
What this page does
Gestational age (GA) is how obstetrics usually counts pregnancy: completed weeks plus leftover days from a dating anchor. That anchor is often the first day of the last menstrual period, an LMP-equivalent built after IVF, or a due date your clinic already locked.
This page returns a clear weeks-and-days string, a trimester hint, and a rough fetal/embryonic-age note (~GA minus two weeks in the classic LMP model) so forum arguments about “how far along” can stop spinning.
Optional IVF transfer mode derives an EDD from day age, then reads GA from that EDD — useful when period apps invent nonsense. It is still planning math. Crown-rump length and clinic redating policy override a browser widget.
When to use
You want today’s GA before an appointment; two apps disagree by four days; you have an EDD and need weeks without mental math in the parking lot.
When not to
Do not override a sonographer’s measurement for medical decisions. If you only want coarse trimester buckets, use the trimester calculator.
Assumptions
From LMP: GA days = asOf − LMP. From EDD: GA days = 280 − (EDD − asOf). IVF path: build EDD from transfer day age, then same as EDD path. Fetal/embryonic age ≈ GA − 14 days shown as an educational note.
Examples
LMP Jan 1, 2026 · as-of Mar 1, 2026 → 8 weeks 3 days. 59 days from LMP.
EDD Nov 26, 2026 · as-of Jul 17, 2026 → 21 weeks 1 day. 280 − days remaining.
Gotchas
Gestational age is not time since conception — fetal age runs ~2 weeks shorter in the classic model.
IVF without an LMP-equivalent looks “wrong” in LMP-only apps — use transfer mode or the IVF LMP-equivalent tool.
Future as-of dates are fine for planning; past as-of helps reconstruct a prior visit.
Estimate only — not medical advice. Confirm dating, testing, and medical decisions with your clinic.
How this is calculated
The math stays in your browser. Enter the dates you actually know, read the estimate, and treat clinic ultrasound dating as the authority when it disagrees.
Nothing here is medical advice, a diagnosis, or a substitute for prenatal care.
- Enter the date(s) or numbers this page asks for.
- Check the assumptions under the result and on Methodology.
- Compare with your clinic portal if you have one.
- Use related tools if you only have a different kind of date.
- Confirm medical decisions with your clinician.
weeks = floor(totalDays / 7), days = totalDays % 7 → display as “12 weeks 3 days.”
Related calculators
Week-focused wording lives on the pregnancy week calculator. LMP-only landing: pregnancy week by LMP. Coarse buckets: trimester calculator.
See also: pregnancy week calculator, trimester calculator, and ivf due date calculator.
FAQ
- How do you calculate gestational age?
- Usually from LMP or EDD: count days, split into weeks + days.
- Is gestational age the same as fetal age?
- No — fetal/embryonic age is typically ~2 weeks less when LMP dating is used.
- Why does my ultrasound say something else?
- Scans can redate; clinical policy wins.
- Can I calculate GA from IVF transfer?
- Yes — we derive EDD from day age, then GA from that EDD.
- What if I only know my due date?
- Use the EDD anchor mode on this page.
- Is this medical advice?
- Estimate only — not medical advice. Confirm dating, testing, and medical decisions with your clinic.