Find Your Estimated Due Date
An OB wheel, also called a pregnancy wheel, estimates your due date from the first day of your last menstrual period (LMP). It is the same simple method doctors have used for decades to date a pregnancy.
Use the free OB Wheel Calculator above to find your estimated due date and your gestational age in seconds. Enter your LMP date, adjust your cycle length if needed, then press Calculate.
Table of Contents
What is an OB Wheel Calculator?
An OB Wheel Calculator is a digital version of the circular pregnancy wheel used in clinics. You enter the first day of your last period, and it estimates your due date and how far along you are today.
Formula - Naegele's rule: EDD = LMP + 280 days + (cycle length - 28 days). Gestational age = days since LMP in weeks+days.
How to Use the OB Wheel Calculator (Step by Step)
- Enter the first day of your last period (LMP).
- Adjust cycle length if not 28 days.
- Press Calculate.
- Note due date and gestational age.
Example Calculation
LMP 1 January 2026, cycle 28 days: due date 8 October 2026.
Features of the OB Wheel Calculator
- Due date + gestational age together
- Cycle-length adjustment
- Based on Naegele's rule used by doctors
- Free, private, no signup
Benefits of Using an OB Wheel Calculator
- Plan pregnancy milestones
- Know your week at a glance
- Same method as the doctor's pregnancy wheel
- Instant result
Final Thoughts
An OB wheel gives you a quick, useful estimate for planning, but always confirm your due date with your doctor. For more free tools, try the TDEE Calculator and the SIP Calculator.
Frequently Asked Questions (FAQs)
How accurate is an OB wheel due date?
Only about 5 percent of babies arrive on the exact due date. The EDD is an estimate; an early ultrasound dating scan is more precise.
What if my cycle is longer than 28 days?
A longer cycle usually means later ovulation, so this calculator adds the extra days (cycle minus 28) to the due date.
Can I use this if I know my conception date?
Yes - set LMP as 14 days before the conception date for a standard 28-day cycle and the result will be very close.
Does this replace medical advice?
No. Always confirm your due date with your doctor or midwife at your first antenatal visit.