Free OB Wheel: Pregnancy Due Date & Gestational Age Calculator

Instant EDD and current gestational age from LMP or ultrasound date. 100% free digital OB wheel for obstetricians, gynaecologists and general practitioners.

The paper OB wheel has been on obstetric desks for 70 years. Our Free OB Wheel is its digital twin — but faster, more accurate, and cycle-length aware.

What is the Free OB Wheel?

A browser-based obstetric calculator from SmartClinic India that gives you EDD, current gestational age (weeks + days), trimester and the antenatal visit schedule — using either LMP (Naegele's rule) or a first-trimester USG.

👉 Open the OB Wheel

How to calculate EDD in 3 steps

Choose dating method — LMP or USG (with CRL/BPD date).
Enter the reference date — LMP first day, or scan date + gestational age reported.
Optionally adjust cycle length — default 28 days; longer cycles push EDD later.

The tool instantly displays EDD, today's gestational age, current trimester and days remaining.

Antenatal visit schedule (WHO / ICMR)

Visit	Gestational age	Key checks
1st ANC	Before 12 weeks	Booking, dating scan, baseline labs
2nd ANC	14 – 26 weeks	Anomaly scan (18–22 wks), OGTT (24–28)
3rd ANC	28 – 34 weeks	Growth scan, Tdap, iron/calcium
4th ANC	36 weeks – term	Presentation, birth-plan review

LMP vs USG dating — which to trust

For patients with irregular cycles or uncertain LMP, an early ultrasound (7–14 weeks) using CRL is the most accurate dating method — accurate to ±5 days. After 14 weeks, USG-based EDD drifts. Our tool lets you enter either, and warns when LMP-derived EDD and USG-derived EDD differ by more than 7 days.

Free tool vs full clinic system

Feature	Free OB Wheel	SmartClinic India
EDD + gestational age	✅	✅
ANC visit reminders on WhatsApp	—	✅
Ante-natal card + growth scan history	—	✅
Print MCP card & delivery summary	—	✅

👉 Create a free clinic account for your OBG practice

Frequently Asked Questions

What is Naegele's rule for EDD?

Add 7 days to the first day of the last menstrual period, subtract 3 months, add 1 year — assuming a 28-day cycle. Total: 280 days from LMP.

How do I adjust EDD for a longer cycle?

Add the number of days beyond 28 to the standard EDD. A 32-day cycle pushes EDD by 4 days. The tool does this automatically.

When should I switch from LMP to USG dating?

When first-trimester USG EDD differs from LMP EDD by more than 7 days, use USG dating. It's more accurate — especially with irregular cycles.

Is the OB Wheel free?

Yes, no signup, no limits. Runs 100% in your browser.

Can patients use it themselves?

Yes — the tool is public and mobile-friendly. Many pregnant women use it to track their week and plan visits.

Does it store any patient data?

No, all calculations are client-side; nothing is uploaded or logged.