Overview
OB Wheel is a free, private pregnancy calculator and complete suite of pregnancy dating tools for expecting parents, clinicians and students. Enter one date you already know — your last menstrual period (LMP), a known due date, an ultrasound measurement, a conception date, or an IVF transfer — and instantly get your estimated due date, gestational age in weeks and days, current trimester, and every key milestone.
What OB Wheel calculates
The main OB wheel calculator works like the pregnancy wheel clinicians spin between patients, but does the maths exactly — accounting for leap years, cycle length and every dating method:
- Due date calculator — your estimated due date from your last period, using Naegele's rule
- Gestational age calculator — how many weeks pregnant you are, from LMP or due date
- CRL calculator — crown-rump length (mm) to gestational age, using the Robinson–Fleming formula
- IVF due date calculator — precise dating from a day-3 or day-5 embryo transfer or egg retrieval
- Conception date calculator — due date from conception, or estimated conception from a due date (also handles IUI)
- Ovulation calculator — your fertile window and most fertile days
- hCG doubling-time calculator — track early-pregnancy hormone rise
- Trimester calculator and weeks-to-months converter — understand where you are in the timeline
- Contraction timer and a gravida/para (TPAL) decoder for later pregnancy and clinical shorthand
Accurate, cited and clear
Every tool follows internationally recognised guidance from sources such as ACOG and the NHS, and each result links to a plain-language guide explaining exactly how the number is calculated — from Naegele's rule to ultrasound dating and the difference between gestational age and fetal age.
Private by design
Every calculation runs entirely in your browser. There are no accounts, no tracking, and nothing you enter is ever stored or sent anywhere. The calculator is also installable and works offline once loaded — handy for clinicians and midwives who need a fast, reliable pregnancy dating tool at the point of care.
Who it's for
Expecting parents who want a quick, trustworthy answer to "when is my due date?" and "how far along am I?"; doctors, midwives and nurses who need fast, accurate obstetric dating between patients; and medical students learning to calculate gestational age and estimated due dates. Free forever, no sign-up required.
