How Many Weeks Pregnant Calculator
Calculate exactly how many weeks pregnant you are using our free UK pregnancy calculator. Whether you know your last menstrual period (LMP), conception date, or have had an ultrasound, we'll tell you your current pregnancy week, trimester, estimated due date, and upcoming NHS appointments.
Enter the first day of your last menstrual period (LMP) - this is the standard method used by the NHS.
If you know your conception date (typically ovulation day or IUI date), enter it here. We'll add 2 weeks to match standard pregnancy dating.
Enter the date of your ultrasound and the gestational age shown on the scan report. This is the most accurate method.
For IVF pregnancies, enter your embryo transfer date and the embryo age at transfer.
NHS Pregnancy Care in the UK
When you discover you're pregnant, contact your GP surgery or a midwife as soon as possible to start your antenatal care. You should have your booking appointment before you're 10 weeks pregnant.
- Booking appointment: Before 10 weeks - health checks, blood tests, discuss options
- Dating scan: 11-14 weeks - confirms due date, checks development
- Anomaly scan: 18-21 weeks - detailed check of baby's organs
- Regular appointments: Throughout pregnancy to monitor your health and baby's growth
Pregnancy Development by Week
Key milestones and developments during each stage of pregnancy:
| Week | Size | Key Developments | NHS Appointments |
|---|---|---|---|
| Week 4-5 | Poppy seed | Positive pregnancy test, embryo implants | Contact GP/midwife |
| Week 6-7 | Lentil | Heart starts beating, brain forming | Book antenatal care |
| Week 8-10 | Raspberry | All major organs forming, fingers/toes | Booking appointment |
| Week 11-14 | Lime | Baby can swallow, facial features form | Dating scan |
| Week 16 | Avocado | May feel first movements (quickening) | 16-week check |
| Week 18-21 | Banana | Can hear sounds, definite movements | Anomaly scan (20 weeks) |
| Week 24 | Corn on the cob | Viability milestone (can survive if born) | - |
| Week 28 | Aubergine | Eyes can open, regular sleep cycles | 28-week check, blood tests |
| Week 32-34 | Pineapple | Practising breathing, gaining weight | 31 & 34-week checks |
| Week 36-37 | Honeydew melon | Head may engage, considered early term | 36-week check |
| Week 38-40 | Watermelon | Full term, ready for birth | 38 & 40-week checks |
Understanding the Three Trimesters
First Trimester (Weeks 1-12)
What's happening: Baby's major organs, brain, spinal cord, and heart are forming. By week 12, baby is about 6cm long.
Common symptoms: Morning sickness, fatigue, breast tenderness, frequent urination, mood changes.
Key scans: Dating scan at 11-14 weeks confirms due date and offers screening tests.
Second Trimester (Weeks 13-26)
What's happening: Rapid growth period. Baby develops fingerprints, can hear, and you may feel movements from 16-24 weeks.
Common symptoms: Energy returns, baby bump shows, possible backache, skin changes, Braxton Hicks.
Key scans: Anomaly scan at 18-21 weeks checks baby's organs in detail.
Third Trimester (Weeks 27-40)
What's happening: Baby gains weight, lungs mature, head may engage. Full term is 37+ weeks.
Common symptoms: Larger bump, breathlessness, heartburn, frequent urination, trouble sleeping, Braxton Hicks intensify.
Preparation: Pack hospital bag, write birth plan, attend antenatal classes.
NHS Antenatal Appointment Schedule
Standard appointment schedule for first pregnancy with no complications:
| Week | Appointment Type | What Happens |
|---|---|---|
| Before 10 weeks | Booking Appointment | Health history, blood tests, urine tests, discuss screening options, calculate due date |
| 11-14 weeks | Dating Scan + Screening | Ultrasound confirms dates, nuchal translucency measurement, combined screening offered |
| 16 weeks | Antenatal Check | Blood pressure, urine, discuss screening results, answer questions |
| 18-21 weeks | Anomaly Scan | Detailed ultrasound checking baby's organs, spine, limbs, face, placenta position |
| 25 weeks | Antenatal Check (first baby only) | Blood pressure, urine, measure bump, check baby's heartbeat |
| 28 weeks | Antenatal Check + Blood Tests | Glucose tolerance if needed, anti-D injection if Rh negative, iron levels |
| 31 weeks | Antenatal Check (first baby only) | Routine checks, discuss birth plan, review blood test results |
| 34 weeks | Antenatal Check | Check baby's position, second anti-D if needed, discuss labour signs |
| 36 weeks | Antenatal Check | Check baby's position (head down?), discuss birth preferences |
| 38 weeks | Antenatal Check | Routine checks, discuss signs of labour, when to contact hospital |
| 40 weeks | Antenatal Check | Discuss options if baby overdue, membrane sweep may be offered |
| 41 weeks | Antenatal Check | Discuss induction, another membrane sweep, monitoring options |
Tips for a Healthy Pregnancy
- Take folic acid - 400 micrograms daily until at least week 12 to prevent neural tube defects
- Take vitamin D - 10 micrograms daily throughout pregnancy and breastfeeding
- Attend all appointments - NHS antenatal care monitors you and baby's health
- Avoid certain foods - Raw meat, unpasteurised cheese, liver, high-mercury fish
- Stay active - Walking, swimming, yoga are safe for most pregnancies
- Monitor baby movements - From 24 weeks, get to know your baby's pattern and report changes
- Stay hydrated - Drink plenty of water to help with common pregnancy symptoms
- Get enough sleep - Rest on your side (left is best) from 28 weeks onwards
Common Pregnancy Dating Mistakes
- Counting from conception - Pregnancy is dated from LMP, not conception (add 2 weeks)
- Using ovulation as LMP - LMP is the first day of your last period, not ovulation
- Expecting exact due dates - Only 4% of babies arrive on their due date; 37-42 weeks is normal
- Ignoring irregular cycles - If cycles vary, ultrasound dating is more accurate than LMP
- Not accounting for IVF - IVF pregnancies need special calculations based on transfer date
- Confusing weeks with months - 40 weeks is approximately 9 months and 1 week, not 10 months
- Missing early appointments - Book with midwife before 10 weeks for proper care
- Ignoring dating scan - The 12-week scan provides the most accurate due date
Frequently Asked Questions
Pregnancy is calculated from the first day of your last menstrual period (LMP), not from conception. Enter your LMP date and the calculator will tell you how many weeks and days pregnant you are. Most pregnancies last 40 weeks (280 days) from LMP, though full term is considered 37-42 weeks. This is the standard method used by the NHS.
The NHS dating scan (also called the 12-week scan or nuchal translucency scan) is usually offered between 11 and 14 weeks of pregnancy. This ultrasound confirms your due date, checks the baby's development, and can offer screening for chromosomal conditions. You'll also be offered the 20-week anomaly scan between 18 and 21 weeks to check baby's organs in detail.
The first trimester is weeks 1-12 when baby's organs develop and morning sickness is common. The second trimester is weeks 13-26 featuring rapid growth and you may feel movements from 16-24 weeks. The third trimester is weeks 27-40 when baby gains weight and prepares for birth. Each trimester lasts approximately 13 weeks.
Due dates are estimates - only about 4% of babies are born on their exact due date. The NHS considers full-term delivery between 37-42 weeks, so most babies arrive within a 5-week window. Your dating scan at 11-14 weeks provides the most accurate due date estimate, often adjusted from your LMP calculation if there's a difference of more than a few days.
Contact your GP surgery or a midwife as soon as you know you're pregnant, ideally before 8 weeks. In the UK, you should have your booking appointment with a midwife before you're 10 weeks pregnant. This is when you'll discuss your antenatal care plan, have initial blood tests and urine tests, and arrange your dating scan.
For IVF pregnancies, the calculation is based on your embryo transfer date rather than LMP. For a 5-day blastocyst transfer, add 19 days to the transfer date to work backwards to your 'LMP equivalent'. For a 3-day embryo transfer, add 17 days. This gives an equivalent LMP date for standard pregnancy dating and due date calculation.
For a first pregnancy with no complications, you'll typically have around 10 antenatal appointments. These include booking (before 10 weeks), dating scan (11-14 weeks), 16-week check, anomaly scan (18-21 weeks), and regular checks at 25, 28, 31, 34, 36, 38, 40, and 41 weeks. Second pregnancies may have fewer appointments if all is straightforward.
Most women feel their baby's first movements (called 'quickening') between 16-24 weeks. First-time mothers often feel movements later (18-24 weeks) than those who've been pregnant before (16-20 weeks). Initially, movements feel like flutters, bubbles, or gentle taps. From 24 weeks, you should monitor your baby's movement pattern daily.
Official UK Resources
NHS - Pregnancy Week by Week
Official NHS guide to each week of pregnancy with development milestones and advice.
Visit NHSNHS - Antenatal Appointments
What to expect at each NHS antenatal appointment throughout your pregnancy.
Visit NHSNHS - Due Date Calculator
Official NHS pregnancy due date calculator based on last menstrual period.
Visit NHSTommy's - Pregnancy Information
UK charity providing evidence-based pregnancy advice and support for parents.
Visit Tommy'sNCT - Pregnancy & Birth
UK's largest charity for parents with pregnancy support, classes, and community.
Visit NCTRCOG - Patient Information
Royal College of Obstetricians & Gynaecologists patient information leaflets.
Visit RCOGRelated Calculators
About This Pregnancy Week Calculator
Our free UK Pregnancy Week Calculator helps expectant mothers and families track their pregnancy journey with accurate, NHS-aligned calculations. Whether you've just discovered you're pregnant or are counting down to your due date, this tool provides the information you need.
Key Features
- Multiple calculation methods - Calculate from LMP, conception date, ultrasound, or IVF transfer
- NHS-aligned dating - Uses the same 40-week calculation as the NHS
- Trimester tracking - Instantly know which trimester you're in
- Appointment schedule - Know when to expect NHS antenatal appointments
- Development milestones - Track your baby's growth week by week
- UK-specific information - All advice based on NHS guidelines
How We Calculate
Pregnancy is counted from the first day of your last menstrual period (LMP), which is typically about 2 weeks before conception. This means when you're "2 weeks pregnant," conception has just occurred. A full-term pregnancy is 40 weeks (280 days) from LMP, though normal delivery can occur anywhere between 37-42 weeks.
Important: This calculator is for informational purposes only and should not replace medical advice. Always attend your NHS antenatal appointments and speak to your midwife or doctor about any concerns. If you experience bleeding, severe pain, reduced movements, or other worrying symptoms, contact your maternity unit immediately.
Pro Tips for Accurate Results
- Double-check your input values before calculating
- Use the correct unit format (metric or imperial)
- For complex calculations, break them into smaller steps
- Bookmark this page for quick future access
Understanding Your Results
Our How Many Weeks Pregnant Calculator provides:
- Instant calculations - Results appear immediately
- Accurate formulas - Based on official UK standards
- Clear explanations - Understand how results are derived
- 2025/26 updated - Using current rates and regulations
Common Questions
Is this calculator free?
Yes, all our calculators are 100% free to use with no registration required.
Are the results accurate?
Our calculators use verified formulas and are regularly updated for accuracy.
Can I use this on mobile?
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