Pregnancy Due Date Calculator
Calculate your estimated due date from your last period or conception date. Track trimester milestones, weeks pregnant and days remaining
Estimated Due Date
Mon Jun 08 2026
38 days away • 5 weeks remaining
Current Pregnancy Progress
34w 3d
Trimester 3rd
Viability (24w)
Mon Feb 16 2026
✓ Reached
Full Term (37w)
Mon May 18 2026
Trimester Milestones
💜 Important Notes
- • Due date is an estimate; most babies arrive within 2 weeks before or after
- • Your healthcare provider may adjust based on ultrasound dating
- • Viability milestone is significant for preterm birth outcomes
- • Regular prenatal care is essential for monitoring pregnancy health
How the Due Date Is Calculated
The standard method uses Naegele's rule: due date equals the first day of your last menstrual period (LMP) plus 280 days, or about 40 weeks. The calculation assumes you ovulated around day 14 of a 28-day cycle and conceived shortly after. If you know the conception date instead (perhaps from IVF or careful tracking), the due date is conception plus 266 days, or 38 weeks.
This is also why pregnancies are dated from LMP rather than conception. The 'gestational age' a midwife uses is roughly 2 weeks ahead of fetal age. So when you are 6 weeks pregnant by NHS dating, the embryo itself is around 4 weeks old. It feels confusing at first but it makes sense once you know that doctors do not know exactly when conception happened, but they usually know when the last period was.
Key Dates Through Pregnancy
| Milestone | Weeks from LMP | What happens |
|---|---|---|
| End of first trimester | 13 weeks | Major organs formed, miscarriage risk drops sharply |
| Anatomy scan | 20 weeks | Detailed scan of organs and growth |
| Viability point | 24 weeks | Baby could survive with intensive medical support |
| Third trimester begins | 28 weeks | Lungs continue maturing, growth accelerates |
| Full term | 37 weeks | Baby is no longer considered preterm |
| Estimated due date | 40 weeks | Average delivery date |
| Post-term | 42 weeks | Induction usually offered |
Why Only 5% of Babies Arrive on Their Due Date
Your due date is a single point in a delivery window that runs from 37 to 42 weeks. Only about 5% of babies actually arrive on the calculated date. Around 80% are born within two weeks either side, and the rest are earlier or later. First babies tend to come a little later than the due date on average; subsequent pregnancies often deliver closer to or slightly before the predicted date.
The earliest dating ultrasound (offered between 8 and 14 weeks at your NHS booking appointment) is usually more accurate than the LMP calculation, particularly if you have irregular cycles or are not certain of your last period date. If the scan date differs from your LMP date by more than 5-7 days, the scan date typically becomes your official due date. Use the [pregnancy week calculator](/pregnancy-week-calculator) to track how far along you are throughout the pregnancy.
Frequently Asked Questions
Is the due date from ultrasound more accurate than from LMP?
Yes, particularly when the scan is done before 14 weeks. Early ultrasounds measure the fetus directly and are accurate to within about 5 days. LMP calculations assume regular cycles and consistent ovulation timing, neither of which everyone has. If your scan date and LMP date differ by more than 5-7 days, the NHS uses the scan date as your official due date going forward.
What if I have irregular cycles?
An LMP-based due date is unreliable if your cycles are over 35 days or vary significantly. Ovulation in long or irregular cycles often happens later than day 14, which makes you less pregnant than the LMP suggests. Always rely on the dating ultrasound at 8-14 weeks rather than LMP if your cycles are not predictable. Mention your cycle pattern to your midwife at the booking appointment.
Can I calculate my due date from IVF transfer?
Yes, and it is more accurate than LMP. For a 5-day frozen embryo transfer, the due date is the transfer date plus 261 days. For a 3-day transfer it is plus 263 days. For a fresh egg-collection cycle it is the egg-collection date plus 266 days. Your fertility clinic will give you the exact figure based on your protocol.
What happens if I go past my due date?
About 1 in 5 first-time mothers reach 41 weeks. The NHS typically offers a membrane sweep at 40-41 weeks and an induction by 41-42 weeks because risks to the baby (placental aging, reduced amniotic fluid) start to rise after 42 weeks. Your midwife will discuss the options at your antenatal appointments. Going a few days past your due date is completely normal and does not on its own indicate a problem.
Related Tools
Pregnancy Week Calculator
Calculate your current pregnancy week and trimester from your due date or last menstrual period. Track baby development milestones.
Pregnancy Milestone Calendar
View your pregnancy milestones week by week. Important developments, screening dates, and what to expect each trimester.
Ovulation Calculator
Calculate your predicted ovulation date based on your menstrual cycle. Identify your fertile window for planning or avoiding pregnancy.