Due Date Calculator
Estimate your due date, pregnancy week and trimesters from your last period
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How It Works: Naegele's Rule
Naegele's rule is the standard way to estimate a due date: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If your cycle is longer or shorter than the standard 28 days, the due date shifts by the same number of days: Due date = LMP + 280 days + (cycle length − 28).
The Three Trimesters at a Glance
| Trimester | Weeks | What happens |
|---|---|---|
| First trimester | Weeks 1–13 | The embryo implants and major organs form; morning sickness is common |
| Second trimester | Weeks 14–27 | Early symptoms usually ease and fetal movements begin; often the most comfortable stage |
| Third trimester | Week 28 to delivery | The baby grows rapidly and the body prepares for delivery |
Good to Know About Due Dates
A due date is only an estimate: only about 5% of babies arrive exactly on that day. Giving birth anytime between 37 and 42 weeks is considered normal (before 37 weeks is preterm, beyond 42 weeks is post-term). Always rely on your healthcare provider's assessment.
Disclaimer
This tool provides an estimate based on Naegele's rule and is for reference only. It does not constitute medical advice. Every pregnancy is different — please consult your doctor or midwife with any questions or concerns.