Free Online Pregnancy Wheel — Calculate Due Date & Gestational Age Instantly
This online pregnancy wheel (OB wheel) calculates your estimated due date (EDD), gestational age in weeks and days, trimester, and key milestones — just like the physical circular gestation wheel used by OB/GYN doctors, but faster and available on any device. Enter your last menstrual period (LMP) below and press Calculate.
Unlike basic due date calculators, ObsCalc is a full obstetric wheel suite with 10+ clinical tools — including fetal weight (Hadlock), Bishop score for induction, VBAC eligibility, newborn Apgar scoring, GDM screening dates, and PPH risk. All tools follow FOGSI, ACOG, RCOG, and WHO guidelines.
Pregnancy Milestones — Week-by-Week Reference (Pregnancy Wheel Guide)
The pregnancy wheel tracks gestation through 40 weeks divided into three trimesters. Use this reference table alongside the pregnancy wheel calculator above to understand what each week means clinically.
| Week | Trimester | Key Milestone / Clinical Event | Approx. EFW |
|---|---|---|---|
| 4–6w | 1st | Implantation, hCG rise, gestational sac on USS | — |
| 7–8w | 1st | Fetal heart activity; best time for dating scan (CRL) | ~1–2 g |
| 11–13w | 1st | NT scan; combined screening (PAPP-A, free β-hCG) | ~20–40 g |
| 13w | 1st | End of 1st trimester; miscarriage risk drops significantly | ~65 g |
| 16–18w | 2nd | Quickening (fetal movements); quad screen | ~150–200 g |
| 18–20w | 2nd | Anomaly scan (level 2 USS); fetal anatomy survey | ~200–300 g |
| 24–28w | 2nd | GDM screening (DIPSI 75g GTT); anti-D for Rh-ve | ~600–1000 g |
| 28w | 2nd | End of 2nd trimester; viability threshold passed | ~1005 g |
| 32–34w | 3rd | Growth scan; high-risk GDM rescreen; GBS swab | ~1700–2150 g |
| 36–37w | 3rd | Late-preterm/early-term; assess presentation, Bishop score | ~2600–2900 g |
| 38–40w | 3rd | Term; EDD at 40w; induction discussion if post-dates | ~3100–3500 g |
| 41–42w | 3rd | Post-dates; CTG monitoring; induction recommended by 42w | ~3400–3700 g |
Pregnancy Wheel vs Due Date Calculator — What's the Difference?
Many patients and even clinicians use "pregnancy wheel," "OB wheel," "due date calculator," and "pregnancy calculator" interchangeably. Here's how they relate and why ObsCalc covers all of them:
| Feature | Physical OB Wheel | Basic Online Calculator | ObsCalc (This Tool) |
|---|---|---|---|
| Due date from LMP | ✓ | ✓ | ✓ + cycle adjustment |
| Gestational age today | ✓ | ✓ | ✓ weeks + days |
| GA from ultrasound scan | ✓ | ✗ | ✓ back-calculates LMP |
| GA on any specific date | ✓ | ✗ | ✓ for op notes |
| Reverse (EDD → LMP) | ✓ | Rarely | ✓ |
| Fetal weight (Hadlock) | Some | ✗ | ✓ 3 & 4 param |
| Bishop score | ✗ | ✗ | ✓ |
| VBAC eligibility | ✗ | ✗ | ✓ FOGSI/ACOG |
| GDM screening dates | ✗ | ✗ | ✓ DIPSI protocol |
| PPH risk score | ✗ | ✗ | ✓ 15 factors |
| WhatsApp / print share | ✗ | Rarely | ✓ |
| Google Calendar link | ✗ | ✗ | ✓ |
| Mobile friendly | Physical | Usually | ✓ Fully responsive |
The physical pregnancy wheel was invented by obstetricians to perform Naegele's Rule calculations at the bedside without mental arithmetic. ObsCalc is its digital equivalent — doing the same calculation plus everything an OB/GYN needs in a single visit.
ObsCalc — Free Online Pregnancy Wheel, OB Wheel & Obstetric Calculator Suite
ObsCalc is the most comprehensive free pregnancy wheel available online. Known clinically as an OB wheel or obstetric wheel, this tool replicates the circular gestation calculator carried by obstetricians, midwives, and OB/GYN doctors — and extends it with 10+ additional clinical calculators built to FOGSI, ACOG, RCOG, and WHO standards. No login. No app download. Works on any phone, tablet, or desktop.
What is a Pregnancy Wheel (OB Wheel)?
A pregnancy wheel — also called an OB wheel, obstetric wheel, or gestational wheel — is a circular slide-rule tool used by healthcare professionals to calculate a pregnant woman's estimated due date (EDD) and gestational age from the first day of her last menstrual period (LMP). It applies Naegele's Rule: EDD = LMP + 280 days (adjusted for cycle length). The physical wheel has been a staple of obstetric practice for over a century. This online pregnancy wheel does the same calculation digitally — instantly, with cycle length adjustment, and with results you can share via WhatsApp or add to your calendar.
When someone searches for "calculator pregnant" or "pregnancy calculator", they are usually looking for one of two things: (1) how many weeks pregnant they are right now, or (2) when their baby is due. The GA by LMP tab above answers both, using the same algorithm as an OB wheel.
Gestational Age Calculators (Pregnancy Wheel)
GA by LMP (Pregnancy Wheel): Enter your LMP and cycle length to get your due date (EDD), gestational age in weeks and days, trimester, conception estimate, and a Google Calendar link for the EDD. This is the core digital pregnancy wheel calculation.
GA by Ultrasound Scan (OB Wheel from Scan): When an ultrasound has already assigned a gestational age, use this tool to back-calculate the LMP, current GA, and EDD. First-trimester ultrasound dating using CRL is more accurate than LMP-based pregnancy wheel calculations, especially for irregular cycles.
GA on Any Given Date: Find exact gestational age on a specified date — essential for operation theatre notes, discharge summaries, birth certificates, and referral letters. Used by OB/GYN doctors exactly as a physical pregnancy wheel would be.
LMP from EDD (Reverse Pregnancy Wheel): Reverse-calculate the LMP and conception date when only the EDD is known — common in referred patients or adopted pregnancies.
Fetal Assessment Tools
Expected Fetal Weight (EFW) — Hadlock 1985: The gold-standard biometric formula used across Indian obstetric practice. Accepts 4 parameters (BPD+HC+AC+FL) or 3 parameters when HC is unavailable. Includes SGA/AGA/LGA classification and ±15% confidence range. Physical pregnancy wheels include fetal weight estimates as a separate ring — this calculator goes further with full Hadlock regression.
Apgar Score Calculator: Score newborn status at 1 minute and 5 minutes post-birth across Appearance, Pulse, Grimace, Activity, and Respiration. Categorises as normal (7–10), moderately depressed (4–6), or severely depressed (0–3) with management guidance.
Obstetric Scoring & Risk Assessment
Bishop Score: Assess cervical favourability for labour induction — score ≥9 allows direct oxytocin; below 6 requires cervical ripening. VBAC/TOLAC Eligibility: 8-point FOGSI/ACOG checklist for trial of labour after caesarean. PPH Risk Assessment: 15-factor weighted scoring per RCOG/FOGSI — stratifies risk from Low to Very High with specific management protocols.
GDM Screening Schedule — DIPSI & FOGSI Protocol
The DIPSI protocol recommends universal non-fasting 75g OGTT for all pregnant Indian women. Blood glucose ≥140 mg/dL at 2 hours = GDM. FOGSI mandates screening at first ANC visit and at 24–28 weeks; high-risk women (BMI ≥25, prior GDM, family history, PCOS) get an additional screen at 32–34 weeks. Enter your LMP and risk factors to receive personalised, calendar-linked screening dates.
Frequently Asked Questions — Pregnancy Wheel & OB Wheel
What is a pregnancy wheel and how does it work?
A pregnancy wheel (OB wheel / obstetric wheel) is a circular tool — physical or digital — that applies Naegele's Rule to calculate gestational age and due date from the last menstrual period. Set the LMP on the wheel, and the corresponding date on the outer ring shows the EDD. This online pregnancy wheel does exactly that calculation in milliseconds, with additional features like cycle-length adjustment, scan-based dating, and milestone tracking.
How many weeks pregnant am I?
Open the "Pregnancy Wheel — Gestational Age" section above, select "GA by LMP", enter your LMP, and press Calculate. The pregnancy wheel will show your gestational age in exact weeks and days. Pregnancy is counted from the first day of your last period — not from the date of conception — which is why you are counted as "2 weeks pregnant" before conception actually occurs.
How accurate is an online pregnancy wheel?
An online pregnancy wheel is as accurate as Naegele's Rule — which assumes a 28-day cycle with ovulation on day 14. For non-standard cycles, use the cycle-length selector to adjust. For the most accurate dating, a first-trimester ultrasound (CRL measurement at 7–12 weeks) is superior. The OB wheel from scan calculator above integrates ultrasound-based dating.
What is the difference between an OB wheel and a due date calculator?
An OB wheel is the clinical name for the physical gestational wheel used by obstetricians. A due date calculator is its digital equivalent. Both use Naegele's Rule. ObsCalc functions as both — a full pregnancy wheel online with additional clinical scoring tools not found on basic due date calculators.
Can I use this pregnancy wheel for cycle lengths other than 28 days?
Yes. The cycle length selector adjusts Naegele's Rule by the difference from 28 days. For a 32-day cycle, 4 extra days are added to the EDD. For a 24-day cycle, 4 days are subtracted. This makes the pregnancy wheel calculator accurate for women with irregular or non-standard cycles.
How is gestational age calculated from LMP?
Using Naegele's Rule, gestational age is calculated by counting days from the first day of the last menstrual period. Each 7 days = 1 week of pregnancy. EDD = LMP + 280 days (for a 28-day cycle). The pregnancy wheel above performs this calculation and displays the result in weeks and days.
Can I use this as an OB wheel for ultrasound-based dating?
Yes. The "GA by Scan" tab acts as an OB wheel from ultrasound. Enter the scan date and the gestational age assigned by the sonographer (in weeks and days). The tool back-calculates your LMP, current gestational age, and EDD — just like an obstetrician would do using the physical obstetric wheel in the clinic.
Which Hadlock formula is used for EFW in India?
The Hadlock 1985 formula is standard in Indian obstetric practice. The 4-parameter formula (BPD+HC+AC+FL) is preferred; the 3-parameter formula (BPD+AC+FL) is used when HC is unavailable. All EFW estimates carry ±15% variability.
What Bishop score indicates a favourable cervix for induction?
Bishop score ≥9: highly favourable — direct oxytocin induction appropriate. Score 6–8: favourable. Score <6: unfavourable — cervical ripening with prostaglandins (PGE2) or Foley catheter recommended before induction.
What is the DIPSI GDM screening protocol?
DIPSI recommends a single-step, non-fasting 75g OGTT. Blood glucose ≥140 mg/dL at 2 hours = GDM. FOGSI recommends universal screening at first ANC visit and 24–28 weeks, with an additional screen at 32–34 weeks for high-risk women.
What are common causes of postpartum hemorrhage (PPH)?
PPH (blood loss ≥500ml vaginal / ≥1000ml cesarean) is most commonly caused by uterine atony — the "4 Ts": Tone, Trauma, Tissue, Thrombin. Active management of the third stage of labour (AMTSL) — oxytocin 10 IU IM at delivery of the anterior shoulder — reduces PPH by up to 50%.