OB Wheel is a fast, free pregnancy dating calculator for expecting parents, clinicians and students. It turns one date you already know into a complete picture of a pregnancy — instantly, and entirely privately.
Enter any one date — your last menstrual period (LMP), a known due date, an ultrasound measurement, a conception or ovulation date, or an IVF embryo transfer — and OB Wheel calculates:
- Your estimated due date, using Naegele's rule and adjusted for your cycle length
- Your gestational age in weeks and days
- Your trimester and the calendar date of every key milestone
- A reverse look-up that answers "when will I be X weeks?"
Beyond the main wheel, the site includes a full suite of dedicated, single-purpose calculators so you can go straight to what you need:
- Gestational age calculator — how far along you are, from LMP or due date
- Due date calculator — a quick estimate from your last period
- 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 transfer, or egg retrieval
- Conception date calculator — works forwards and backwards, and handles IUI
- hCG doubling-time calculator — track early-pregnancy hormone rise
- Ovulation & fertile-window calculator — plan around your most fertile days
- Trimester calculator and weeks-to-months converter — understand the timeline
- Contraction timer and a gravida/para (TPAL) decoder for later stages and clinical shorthand
Every tool follows recognised guidance from sources like ACOG and the NHS, and each explains its method transparently.
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 site is also installable and works offline once loaded — handy for clinicians at the point of care.
