Pregnancy Due Date Calculator
Calculate your pregnancy due date from your last menstrual period or IVF transfer date. See current week, trimester, and key milestones.
Pregnancy Due Date Calculator
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The pregnancy due date calculator works out your estimated due date (EDD) using Naegele's rule — the standard method used by obstetricians and midwives worldwide. Enter your last menstrual period (LMP) date or your IVF transfer date, and the calculator returns your due date, how many weeks pregnant you are today, your current trimester, and a timeline of key pregnancy milestones. Naegele's rule calculates your due date by adding 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle — for longer or shorter cycles, the due date shifts accordingly. The 280-day figure represents the average full-term pregnancy duration, measured from the LMP rather than the conception date (which is typically estimated at around two weeks after the LMP for a 28-day cycle). Your healthcare provider may adjust your due date based on ultrasound measurements, particularly the dating scan at 10–13 weeks. Ultrasound dating is generally more accurate than LMP dating when periods are irregular. This calculator gives you a solid baseline estimate before or between appointments.
How to Use the Pregnancy Due Date Calculator
The Pregnancy Due Date Calculator is designed to give you an accurate answer in seconds. Follow these steps:
- 1Enter your details into the input fields above.
- 2Adjust any settings, toggles, or unit selections to match your situation.
- 3Your results appear automatically — review the output and adjust any inputs to explore different scenarios.
No account or sign-up required. All calculations run locally in your browser — nothing is stored or transmitted to any server.
How It Works
Due Date = LMP + 280 days (adjusted for cycle length) | IVF 5-day: Transfer + 266 days
LMP Method (most common): Due Date = LMP + 280 days For cycles other than 28 days, the formula adjusts: Due Date = LMP + 280 + (Cycle Length − 28) days. A 35-day cycle pushes the due date 7 days later than a 28-day cycle. IVF Method: - 5-day blastocyst transfer: Add 266 days (38 weeks) to transfer date - 3-day embryo transfer: Add 268 days to transfer date The difference reflects that embryo age is already known precisely with IVF — a 5-day blastocyst is already 5 days past fertilisation, so it reaches 40 gestational weeks in 266 days from transfer. Example: LMP = 1 January 2025, 28-day cycle. Due date = 1 January + 280 days = 8 October 2025 At 8 weeks pregnant today (1 March 2025), you are in the first trimester.
Frequently Asked Questions
How accurate is the due date calculator?
The LMP-based calculation is accurate to within ±2 weeks for women with regular 28-day cycles. Only about 4–5% of babies are born on their exact due date; most arrive within 2 weeks either side. First ultrasound dating (at 10–13 weeks) is typically more precise and your healthcare provider may revise the due date based on crown-rump length measurements. Irregular periods reduce the accuracy of LMP-based dating significantly.
What trimester am I in?
Pregnancy is divided into three trimesters: First trimester: 0–13 weeks (weeks 1–13). This is the period of most rapid early development. Second trimester: 14–26 weeks (weeks 14–26). Often called the "honeymoon trimester" — nausea typically eases and energy returns. Third trimester: 27–40+ weeks (weeks 27 onwards). Final organ maturation and growth; most weight gain occurs here. The calculator shows your current trimester based on today's date and your LMP.
How is an IVF due date calculated?
For IVF pregnancies, the due date is calculated from the embryo transfer date rather than the LMP. A 5-day blastocyst transfer: add 266 days. A 3-day embryo transfer: add 268 days. These figures account for the known age of the embryo at transfer. IVF due dates are typically very accurate because the fertilisation date is precisely known.
Should I use LMP or ultrasound for my due date?
Both — but defer to the ultrasound date when the two differ by more than 5–7 days. LMP-based dating is a good starting estimate but assumes a regular 28-day cycle and accurately recalled period dates. First-trimester ultrasound (10–13 weeks) measures the baby's size and is accurate to ±5 days — it is the gold standard for establishing gestational age and due date when there is any uncertainty about the LMP.
What happens at 40 weeks of pregnancy?
40 weeks is the estimated due date — not an expiry date. Only about 4–5% of babies arrive exactly on their due date. Most clinicians consider 37–42 weeks to be "full term." If labour has not started by 41–42 weeks, your healthcare provider may recommend induction to reduce risks associated with post-dates pregnancy. Your care team will monitor you closely in the final weeks and discuss options based on your individual circumstances.