Due Date Calculator UK 2025
Calculate your baby's estimated due date with NHS guidance
Calculate from Last Menstrual Period
Enter the first day of your last menstrual period (LMP) to calculate your estimated due date using Naegele's Rule.
Calculate from Conception Date
If you know when you conceived, enter that date to calculate your due date (conception + 266 days = 38 weeks).
When did conception occur?
Conception typically occurs 12-24 hours after ovulation. If you tracked ovulation using OPKs, temperature charting, or fertility apps, your conception date is likely within 1-2 days of your positive ovulation test.
IVF & Fertility Treatment Calculator
For IVF pregnancies, enter your embryo transfer date and type for precise due date calculation.
How IVF Due Dates Work
For IVF pregnancies, we calculate an "artificial LMP" by backdating from your transfer date. For a Day 5 blastocyst, we subtract 19 days to get your equivalent LMP, then add 280 days for the due date.
Calculate from Dating Scan
If you've had your NHS dating scan, enter the scan date and gestational age given to calculate your due date.
Dating Scan Accuracy
NHS dating scans performed between 10-14 weeks measure your baby's crown-rump length (CRL) and are accurate to within ±5 days. This is considered the most reliable method for establishing your due date.
Understanding Pregnancy Due Dates in the UK
Your estimated due date (EDD) is one of the most important dates of your pregnancy, helping you and the NHS plan your antenatal care and prepare for your baby's arrival. However, it's important to understand that only about 5% of babies arrive on their exact due date - most are born within 2 weeks either side.
How Naegele's Rule Works
The standard method for calculating due dates, Naegele's Rule, was developed by German obstetrician Franz Naegele in the early 19th century. It works by:
- Taking the first day of your last menstrual period (LMP)
- Adding 280 days (40 weeks or approximately 9 months and 7 days)
- Adjusting for cycle length if different from 28 days
Why 40 Weeks?
Pregnancy is dated from the first day of your LMP, not from conception (which occurs about 2 weeks later). This means when you're "4 weeks pregnant," your baby has only existed for approximately 2 weeks. The 40-week timeline is a convenient way to track pregnancy from a known date.
NHS Dating Scan
The NHS offers all pregnant women a dating scan between 10-14 weeks of pregnancy. This ultrasound scan:
- Measures your baby's crown-rump length (CRL)
- Provides an estimated due date accurate to ±5 days
- Checks for multiple pregnancies
- Can be combined with screening for Down's syndrome
If the scan date differs from your LMP-based date by more than 7 days, the NHS will use the scan date as your official due date for all future appointments.
Factors Affecting Due Date Accuracy
| Factor | Effect on Accuracy | Solution |
|---|---|---|
| Irregular cycles | LMP calculation may be off by days or weeks | Dating scan provides accurate date |
| Unknown LMP date | Cannot calculate from LMP | Dating scan essential |
| Recent contraception | Cycles may not be regular yet | Dating scan recommended |
| Long cycles (>35 days) | Ovulation occurs later, LMP date too early | Adjust for cycle length or use scan |
| Short cycles (<25 days) | Ovulation occurs earlier, LMP date too late | Adjust for cycle length or use scan |
NHS Antenatal Care Pathway
Once you discover you're pregnant, the NHS provides structured antenatal care throughout your pregnancy. Your due date determines the timing of all appointments and scans.
Key Appointments by Week
| Weeks | Appointment | What Happens |
|---|---|---|
| 8-12 | Booking Appointment | Medical history, blood tests, discuss care options |
| 10-14 | Dating Scan | Confirm due date, check development, screening option |
| 18-21 | Anomaly Scan | Detailed check of baby's organs and development |
| 25 | Midwife Check | Blood pressure, urine, discuss birth plan |
| 28 | Midwife + Bloods | Check for anaemia, antibodies, discuss feeding |
| 31-34 | Regular Appointments | Monitor growth, position, prepare for birth |
| 36 | Position Check | Check baby's position, discuss birth options |
| 38-41 | Final Appointments | Membrane sweeps offered, induction discussion |
What If You Go Past Your Due Date?
Post-Dates Pregnancy Management
Going past your due date is common - about 50% of first-time mothers go past 40 weeks. The NHS has a structured approach:
- 40 weeks: Membrane sweep offered to encourage labour
- 41 weeks: Another sweep offered, induction appointment booked
- 41+3 to 41+5: Induction typically scheduled
- 42 weeks: Strong recommendation for induction (risks increase)
UK Maternity Rights and Leave
Understanding your maternity rights helps you plan your pregnancy timeline. Your due date determines when you can start maternity leave and when benefits begin.
Statutory Maternity Leave
- Total entitlement: Up to 52 weeks (26 weeks ordinary + 26 weeks additional)
- Earliest start: 11 weeks before due date (week 29)
- Compulsory leave: Minimum 2 weeks after birth (4 weeks for factory workers)
- Automatic trigger: If baby born before leave starts, leave begins from birth date
Statutory Maternity Pay (SMP) 2025/26
| Period | Payment | Duration |
|---|---|---|
| First 6 weeks | 90% of average weekly earnings | Weeks 1-6 |
| Remaining weeks | £184.03/week or 90% (whichever is lower) | Weeks 7-39 |
| Additional leave | Unpaid | Weeks 40-52 |
Shared Parental Leave
Parents can share up to 50 weeks of leave and 37 weeks of pay between them. This gives flexibility for both parents to take time with the baby. To qualify:
- Mother must end maternity leave early (at least 2 weeks after birth)
- Remaining leave and pay can be shared with partner
- Can be taken at different times, same time, or in blocks
- Must give 8 weeks' notice for each block of leave
Other Benefits to Consider
- Child Benefit: £25.60/week for first child, £16.95 for additional children
- Sure Start Maternity Grant: £500 one-off payment (if on certain benefits)
- Tax-Free Childcare: Up to £2,000/year per child towards childcare costs
- 30 Hours Free Childcare: For 3-4 year olds (working parents)
Pregnancy Trimester Guide
First Trimester (Weeks 1-12)
The most critical period for your baby's development. All major organs begin forming, and by week 12 your baby has a recognisable human form with fingers and toes.
What to Expect
- Morning sickness peaks around weeks 8-10
- Extreme tiredness is normal
- Breast tenderness and changes
- Frequent urination
- Heightened sense of smell
Second Trimester (Weeks 13-26)
Often called the "honeymoon period" as morning sickness typically subsides and energy returns. You'll feel your baby's first movements (quickening) between weeks 16-22.
Key Milestones
- Baby bump becomes visible
- Feel first movements (16-22 weeks)
- Anomaly scan at 18-21 weeks
- May find out baby's sex (if desired)
- Energy levels improve
Third Trimester (Weeks 27-40)
Your baby gains significant weight and prepares for birth. You'll attend more frequent appointments and may experience Braxton Hicks contractions as your body prepares for labour.
Preparing for Birth
- Pack hospital bag by week 36
- Write birth plan
- Install car seat
- Prepare nursery
- Attend antenatal classes
Frequently Asked Questions
Contact your GP or local midwifery service as soon as you get a positive pregnancy test. This allows them to book your first midwife appointment (booking appointment) for around 8-12 weeks. Early contact ensures you don't miss important early scans and screening tests. You'll receive your maternity notes at your booking appointment.
Calculators based on LMP are accurate to within about 7-14 days for women with regular 28-day cycles. However, only 5% of babies arrive on their exact due date. The NHS dating scan (10-14 weeks) is more accurate at ±5 days as it measures actual fetal size. Think of your due date as an estimate - your baby could arrive anytime between 37-42 weeks, which is all considered full term.
If your dating scan shows your baby measures more than 7 days different from your LMP-calculated date, the NHS will adjust your due date to match the scan. This commonly happens if you have irregular cycles, didn't ovulate on day 14, or aren't certain of your LMP date. The scan date becomes your official due date for all future appointments.
If you're unsure of your LMP date (common with irregular periods or recent contraception), don't worry. The NHS dating scan will establish your due date based on your baby's measurements. Contact your midwife early, explain the situation, and they may book an earlier scan to date your pregnancy. Many women in this situation get accurate due dates from their scans.
Statutory maternity leave can start from 11 weeks before your due date (week 29 of pregnancy). Most women start between 36-38 weeks to have some rest time before birth. Your leave automatically starts if your baby arrives early or if you're off work with a pregnancy-related illness in the 4 weeks before your due date. You must give your employer at least 15 weeks' notice of your intended start date.
Yes, statistically first babies arrive later on average. The average first baby arrives at 40 weeks and 5 days - about 5 days after the due date. About 50% of first-time mothers go past their due date. Subsequent babies tend to arrive slightly earlier (average 40+3). However, individual variation is significant, so don't rely on this as a rule.
A membrane sweep is a vaginal examination where the midwife separates the membranes around your baby from your cervix, releasing prostaglandins that may trigger labour. It's offered at 40 weeks for first babies and can be repeated at 41 weeks. It's uncomfortable but not usually painful. About 1 in 8 sweeps successfully triggers labour within 48 hours. You can decline if you prefer to wait for natural labour.
NHS guidance recommends offering induction between 41 and 42 weeks of pregnancy. You'll typically be offered an induction appointment for around 41+3 to 41+5 weeks. Going beyond 42 weeks increases certain risks (placental insufficiency, reduced amniotic fluid), so induction is strongly recommended by this point. However, induction is always your choice - you can discuss the benefits and risks with your midwife and make an informed decision.
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 Due Date 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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