Pregnancy Due Date Calculator
Pick the first day of your last period and your usual cycle length. You get your estimated due date, how far along you are, and your trimester.
How is the due date calculated?
Doctors use Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. The rule assumes a 28-day cycle, so a longer or shorter cycle moves the date by the difference, and this calculator adjusts for it.
Example: your last period started on 1 January 2026 and your cycle is 28 days. Your due date is 1 January + 280 days = 8 October 2026.
| Trimester | Weeks |
|---|---|
| First | 1 to 13 |
| Second | 14 to 27 |
| Third | 28 to 40 |
Only about 4% of babies arrive on their due date; birth between weeks 37 and 42 is normal. This is an estimate and does not replace your doctor's advice.
Frequently asked questions
How do I calculate my due date?
How many weeks is a full-term pregnancy?
Is an ultrasound due date more accurate?
Results are estimates for guidance and do not replace the official authority or professional advice.