Pregnancy week by LMP
If you still have a real last period (not an IVF equivalent), this is the straight path: LMP in, weeks + days out. Estimate only — not medical advice.
Enter a date to see an estimate.
What this page does
Classic spontaneous-pregnancy landing. We keep the form LMP-first so you are not hunting for an EDD toggle.
Cycle length notes belong more on LMP due date / the EDD workbench when you are estimating ovulation day — GA from a stated LMP is simply days since that LMP unless a clinic redates.
When to use
Classic spontaneous pregnancy; first prenatal questionnaire; you trust LMP more than a guessed EDD.
When not to
IVF / no real LMP → IVF LMP equivalent or transfer dating. Spotting that may not be a true period — ask the clinic.
Assumptions
Browser-only planning arithmetic. Defaults are disclosed on the page. Ultrasound and clinic policy override this tool.
Examples
LMP Mar 3, 2026 · today Jul 17, 2026 → 19 weeks 3 days.
LMP Mar 3, 2026 · cycle note 35 days → GA from LMP unchanged; ovulation note shifts.
Gotchas
Clinic dating after ultrasound can differ from browser math — the clinic wins for medical decisions.
Wrong input dates (retrieval vs transfer, spotting vs true LMP) slide every result.
Estimate only — not medical advice.
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.
GA = asOf − LMP → weeks/days.
Related calculators
EDD-first weeks: pregnancy week calculator. EDD from LMP: LMP due date. Multi-mode: EDD calculator.
See also: lmp due date calculator, gestational age calculator, and pregnancy week calculator.
FAQ
- How do I calculate pregnancy weeks from LMP?
- Count days from LMP to today; divide by 7.
- What if my cycle is irregular?
- LMP dating is shakier; ultrasound may take over.
- Is day 1 the first day of bleeding?
- Usually first full-flow day — follow your clinic’s definition.
- Can I enter an IVF LMP-equivalent?
- Yes, if you built one on purpose.
- Implantation bleeding?
- Mistaking it for LMP shifts everything by a week+.
- Is this medical advice?
- Estimate only — not medical advice. Confirm dating, testing, and medical decisions with your clinic.