Find your estimated due date, how many weeks along you are, your trimester and conception date — with a week-by-week timeline. Works from your last period, conception date, IVF transfer or a known due date.
Dates are estimates based on a 40-week (280-day) pregnancy. Your healthcare provider may adjust them after an ultrasound. This tool does not provide medical advice.
A pregnancy due date calculator estimates when your baby will arrive based on standardised medical timelines. A typical human pregnancy lasts approximately 40 weeks (280 days) measured from the first day of your last menstrual period (LMP). Because fewer than 5% of babies are born on their exact estimated due date (EDD), it is best to treat the date as a reliable anchor point for planning your trimesters, medical checkups and lifestyle changes — not a fixed deadline.
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Healthcare professionals use a few distinct methods to pinpoint a due date. This calculator lets you enter whichever information you have most readily available.
| Method | How it is calculated | Notes |
|---|---|---|
| Last period (LMP) | Naegele's rule: first day of last period + 7 days − 3 months + 1 year (about 280 days) | The standard OB-GYN baseline; assumes a 28-day cycle with conception near day 14. |
| Conception date | Conception date + 266 days | Useful if you tracked ovulation or used fertility apps. |
| IVF transfer (day 3) | Transfer date + 263 days | Embryo age is known, so dating is highly precise. |
| IVF transfer (day 5) | Transfer date + 261 days | Blastocyst transfer; also very precise. |
| Known due date | Works backwards from your EDD | Shows your current week and trimester. |
Once your estimated due date is calculated, your pregnancy timeline breaks down into three fundamental stages.
| Trimester | Timing | Key developmental milestones |
|---|---|---|
| First trimester | Weeks 1–12 | The foundational phase: the embryo develops vital systems, a heartbeat begins, and early pregnancy symptoms appear. |
| Second trimester | Weeks 13–27 | Often called the "golden phase": energy typically returns, the bump becomes visible, and you may feel the first flutters of movement. |
| Third trimester | Week 28 to birth | The final stretch of rapid growth: the baby moves lower into the pelvis to prepare for labour as the lungs finish developing. |
While 40 weeks is the target, a healthy birth is categorised by the exact week of delivery:
| Category | Timing |
|---|---|
| Early term | 37 weeks 0 days – 38 weeks 6 days |
| Full term | 39 weeks 0 days – 40 weeks 6 days |
| Late term | 41 weeks 0 days – 41 weeks 6 days |
| Post-term | 42 weeks 0 days and beyond |
Gestational age is measured from the first day of your last period and is the standard way pregnancy is described, so at conception you are already counted as about two weeks pregnant. Fetal (conceptional) age is measured from conception itself and is roughly two weeks less. This calculator reports gestational age, the figure your provider will use.
A due date is a best estimate, not a guarantee. Only around one in twenty babies arrives on the exact date, and a healthy birth can occur across several weeks. Early ultrasound dating, usually performed between weeks 8 and 12, measures the crown-rump length of the embryo and is generally the most reliable way to confirm or adjust your dates.
A typical pregnancy lasts about 280 days (40 weeks) from the first day of your last period, which is the basis of Naegele's rule. If you know your conception date the tool adds 266 days, and for IVF it counts from the transfer date using the embryo's age.
Yes. It is common for a practitioner to adjust your official due date in the first trimester. An early dating ultrasound, usually between weeks 8 and 12, measures the crown-rump length of the embryo, and if it differs significantly from your period math the ultrasound date becomes the clinical standard.
If your cycles are consistently shorter or longer than 28 days, calendar math can be slightly off. Entering your average cycle length helps the calculator adjust the estimate, but a first-trimester dating ultrasound remains the most definitive way to confirm your timeline.
Delivery is categorised by the exact week of birth: early term is 37w0d–38w6d, full term is 39w0d–40w6d, late term is 41w0d–41w6d, and post-term is 42 weeks and beyond.
Gestational age is counted from the first day of your last period and includes about two weeks before conception. Fetal age is counted from conception and is roughly two weeks less. Pregnancy is normally described using gestational age.
Yes. Choose the IVF transfer option and select a day-3 or day-5 transfer. For a day-3 embryo the calculator counts forward 263 days, and for a day-5 blastocyst it counts 261 days, making IVF dating very precise.
Dating follows the widely used Naegele's rule and standard obstetric definitions of gestational age, trimesters and term. For trusted, detailed guidance see the American College of Obstetricians and Gynecologists (ACOG) and the NHS pregnancy information. This page is general information, not medical advice.