LMP due date calculator
Classic path: first day of the last period, add about 280 days (Naegele-style for 28-day cycles). Optional cycle length shifts the estimate when you do not ovulate on day 14. Estimate only — not medical advice.
Enter a date to see an estimate.
What this page does
Straight landing for people who still have a real LMP. Cycle adjustment uses EDD ≈ LMP + 280 + (cycleLength − 28).
IVF without a real period should not invent menses here — use IVF due date or LMP-equivalent tools instead.
When to use
Spontaneous pregnancy; first DIY estimate; comparing cycle 28 vs 32.
When not to
IVF without real LMP. Known ovulation that contradicts LMP — prefer ovulation → EDD.
Assumptions
Browser-only planning arithmetic. Defaults are disclosed on the page. Ultrasound and clinic policy override this tool.
Examples
LMP Jul 1, 2026 · cycle 28 → EDD Apr 7, 2027.
LMP Jul 1, 2026 · cycle 30 → EDD Apr 9, 2027.
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.
EDD = LMP + 280 + (cycleLength − 28); default cycle 28.
Related calculators
Multi-mode: EDD calculator. Weeks from same LMP: week by LMP. Reverse: reverse due date.
See also: edd calculator, pregnancy week by lmp calculator, and ovulation to due date calculator.
FAQ
- What is Naegele’s rule?
- A traditional LMP-based due date shortcut.
- How does cycle length change due date?
- Longer cycles usually push EDD later in simple models.
- Should I change my clinic EDD with this?
- No — planning only.
- What if I don’t remember LMP?
- Use reverse, ovulation mode, or clinic records.
- Short luteal phases?
- They break “cycle − 28” simplicity — disclosed.
- Is this medical advice?
- Estimate only — not medical advice. Confirm dating, testing, and medical decisions with your clinic.