Milestone dates for this pregnancy
| Gestational age | Date | Milestone |
|---|
The row for the current week is highlighted. EDD = LMP + 280 days (Naegele's rule); trimesters per ACOG: first up to 13 w 6 d, second 14 w 0 d – 27 w 6 d, third from 28 w 0 d.
Reverse calculator: known gestational age on a date
"The patient was 12 w 0 d on March 3rd" — reconstruct the LMP and the due date.
One screen with every date, editable in both directions, plus ACOG ultrasound redating, IVF transfer dating and the Bishop score. No account, no patient data stored, works offline.
Get Partus on the App StoreCommon questions
How is the due date calculated?
By Naegele's rule: the estimated due date (EDD) is 280 days — 40 weeks — after the first day of the last menstrual period, assuming a 28-day cycle with ovulation on day 14. From a conception date, the EDD is conception + 266 days.
What if the ultrasound disagrees with these dates?
ACOG defines thresholds for when ultrasound dating should replace LMP dating. Check the difference in our free ACOG redating calculator.
Gestational age vs. fetal age — what's the difference?
Gestational age counts from the LMP; fetal (embryonic) age counts from conception and is about two weeks less. Clinical dating uses gestational age.
What about IVF pregnancies?
IVF pregnancies are dated from the embryo transfer: EDD = transfer date + 263 days (day-3), + 261 days (day-5) or + 260 days (day-6). No LMP is needed. The Partus app computes these directly.
How accurate is a pregnancy wheel?
A physical wheel is read to roughly ±1–2 days because of its printed scale; this calculator does the same arithmetic exactly. Dating accuracy itself depends on how the pregnancy is dated — early ultrasound is accurate to about ±5–7 days, LMP recall varies more.
Source
Methods for Estimating the Due Date. ACOG Committee Opinion No. 700, May 2017. This page is a reference tool for healthcare professionals. It does not provide medical advice or diagnosis.