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Pregnancy Due Date Calculator
Enter your last menstrual period date or conception date to calculate your due date, current week, trimester, and key pregnancy milestones. Includes a gentle medical disclaimer.
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How to use the Pregnancy Due Date Calculator
Choose your calculation method
Select 'Last period date' to use the first day of your last menstrual period (LMP), or 'Conception date' if you know when conception occurred.
Enter the date
Pick the date using the date selector. The calculator will immediately show your estimated due date, current week, trimester, and pregnancy progress.
Check your milestones
Scroll down to see key pregnancy milestones week by week — from the first heartbeat scan to full-term status — with the date each milestone falls on.
Note the disclaimer
This calculator provides an estimate. Always confirm your due date with your midwife or doctor using an early ultrasound scan.
About this Pregnancy Due Date Calculator
Calculating a due date is one of the first things expectant parents want to do after a positive pregnancy test. The most widely used method is Naegele's Rule, developed by Franz Naegele in 1812: add 280 days (40 weeks) to the first day of the last menstrual period. This assumes a regular 28-day cycle with ovulation occurring around day 14. In practice, every pregnancy is different. Cycle length varies, ovulation timing varies, and implantation timing varies. This is why only about 5% of babies arrive on their exact estimated due date — most arrive within two weeks either side. A baby born between 37 and 42 weeks is considered normal. The most accurate way to date a pregnancy is an early ultrasound scan, typically offered between 10 and 14 weeks. This measures the baby's crown-rump length to estimate gestational age. If your scan date differs significantly from your LMP date, your healthcare provider will usually adjust your due date based on the scan. The milestones in our calculator are based on typical developmental timelines. Your healthcare team will monitor these at scheduled scans and appointments. If you have concerns about your pregnancy at any stage, always contact your midwife, GP, or hospital.
Frequently Asked Questions
The standard method uses Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a regular 28-day cycle. If you know your conception date, add 266 days instead. Our calculator uses both methods.
Due date calculators give an estimated due date (EDD). Only around 5% of babies are born on their exact due date. Most births happen between 38 and 42 weeks. An early ultrasound scan (before 13 weeks) is the most accurate way to confirm your due date.
The first trimester runs from week 1 to 12 (months 1–3). The second trimester is weeks 13 to 26 (months 4–6). The third trimester is weeks 27 to 40+ (months 7–9). Each trimester brings different developmental milestones for the baby and physical changes for the mother.
Full-term pregnancy is defined as 39 to 40 weeks and 6 days. Early-term is 37–38 weeks. Late-term is 41 weeks. Post-term is 42 weeks or beyond. The terms 'premature' or 'preterm' apply to births before 37 weeks. Babies born at full term generally have the best health outcomes.