Pregnancy Due Date Calculator
Calculate your baby’s estimated due date from your last period, conception date, or IVF transfer. Get your trimester dates, key milestones, and a personalised week-by-week timeline instantly.
Due Date Calculator
Calculate your estimated due date and pregnancy milestones
The most common method uses the first day of your last period
Enter the date your last period started
Adjust if your cycle is not 28 days
Your Pregnancy Details
Estimated due date, milestones and trimester dates
Select your calculation method, enter the date, then click Calculate Due Date to see your estimated due date and pregnancy timeline.
Pregnancy Week by Week
Key development stages and what to expect each trimester.
| Trimester | Weeks | Key Milestone | Typical Symptoms |
|---|---|---|---|
| First Trimester | 1–4 | Implantation, positive test | Fatigue, missed period |
| First Trimester | 5–8 | Heartbeat detectable by scan | Morning sickness, breast tenderness |
| First Trimester | 9–13 | All major organs formed, nuchal scan | Nausea easing, first scan |
| Second Trimester | 14–18 | Baby begins to move | Energy returns, bump shows |
| Second Trimester | 19–22 | Anatomy scan (20-week scan) | Kicks felt, gender possible |
| Second Trimester | 23–27 | Viability milestone at 24 weeks | Back ache, Braxton Hicks begin |
| Third Trimester | 28–32 | Baby’s eyes open; rapid growth | Shortness of breath, frequent urination |
| Third Trimester | 33–36 | Baby turns head-down (engagement) | Pelvic pressure, nesting instinct |
| Third Trimester | 37–40 | Full term at 37 weeks, birth | Cervical changes, labour signs |
Due Date Calculator FAQ
Everything you need to know about calculating your due date and understanding your pregnancy timeline.
Your estimated due date (EDD) is typically calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This is known as Naegele’s rule. If you know your conception date, 266 days (38 weeks) are added instead. Your healthcare provider may adjust this date based on early ultrasound measurements, which are often more accurate than LMP-based calculation.
Due date calculators are a good estimate, but only about 4% of babies are born on their exact due date. Most babies arrive within two weeks either side of the EDD. An early dating ultrasound (between 8–14 weeks) is more accurate than LMP-based calculation, especially if your cycles are irregular. Your midwife or obstetrician will confirm your EDD at your booking appointment.
The first trimester runs from week 1 to week 13 — a critical period of organ development. The second trimester runs from week 14 to week 27 — usually the most comfortable period, when you’ll feel your baby move. The third trimester runs from week 28 to week 40 (or delivery) — a time of rapid growth and preparation for birth. Each trimester brings different developmental milestones and symptoms.
The standard Naegele’s rule assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, your due date may differ. This calculator adjusts automatically — if you have a 35-day cycle, 7 extra days are added to the LMP-based due date. You can select your average cycle length from the dropdown to get a more accurate result.
For IVF pregnancies, the due date is calculated from the embryo transfer date. For a Day 3 transfer, 263 days are added. For a Day 5 (blastocyst) transfer, 261 days are added. These calculations account for the embryo’s age at transfer. This calculator supports all IVF transfer types — simply select the appropriate option from the method dropdown.
A full-term pregnancy is defined as 39 to 40 weeks and 6 days. Babies born at 37–38 weeks are considered early term, and those born at 41+ weeks are late term. Most healthcare providers will recommend induction by 42 weeks. Babies born before 37 weeks are considered premature (preterm). The due date is calculated at 40 weeks exactly.
In the UK, most women are offered two routine ultrasound scans during pregnancy. The dating scan takes place between 8 and 14 weeks, and the anatomy scan (mid-pregnancy scan) takes place between 18 and 21 weeks. The dating scan is used to confirm gestational age and update your due date if it differs significantly from your LMP-based calculation.
Gestational age is counted from the first day of your last menstrual period — so at conception (around week 2), you’re already considered 2 weeks pregnant. Foetal age (or embryonic age) counts from the actual date of conception, so it is approximately 2 weeks less than gestational age. Healthcare providers always use gestational age, which is what this calculator displays.