This pregnancy due date calculator estimates your baby’s due date from the first day of your last menstrual period (LMP). It also shows how many weeks pregnant you are today, your trimester and the approximate date of conception.
How the due date is calculated
The calculator uses Naegele’s rule: due date = LMP + 280 days (40 weeks). This assumes a 28-day cycle. If your cycle is longer or shorter, the due date is moved later or earlier by the difference — for a 32-day cycle, 4 days later.
Example
If your last period started on 1 January 2026 and your cycle is 28 days, the estimated due date is 8 October 2026.
Trimesters at a glance
- First trimester: week 1 to the end of week 12.
- Second trimester: week 13 to the end of week 26.
- Third trimester: week 27 until birth.
Frequently asked questions
How accurate is the due date?
It is an estimate. Only a small share of babies are born on their exact due date; most arrive within about two weeks either side. An early ultrasound scan usually gives a more reliable date, and your doctor may adjust your due date based on it.
When should I see a doctor?
Book antenatal care as soon as you know you are pregnant. Seek urgent care for heavy bleeding, severe abdominal pain, severe headache with blurred vision, or if your baby’s movements reduce.
Disclaimer: this tool is for general information only and is not medical advice. Always follow your doctor or midwife’s guidance.