Due Date Calculator
Use this due date calculator to estimate a pregnancy due date, conception date, and trimester milestones from the first day of the last menstrual period.
Pregnancy dates are estimates. Your clinician may adjust dates after an ultrasound.
How it's calculated
Due date = first day of last period + 280 days
The 280-day estimate assumes a 28-day cycle. If your cycle is longer or shorter, ovulation may happen later or earlier, which shifts the estimate.
What your result means
| Category | Range | What it means |
|---|---|---|
| LMP method | Last period + 280 days | The common calendar method used for an initial estimate. |
| Conception method | Conception + 266 days | Useful when conception timing is known more clearly. |
| Ultrasound dating | Clinical estimate | Often used to refine or confirm dates. |
Due dates are estimates
Only a small share of babies arrive exactly on their due date. Think of it as the center of a likely birth window.
Cycle length matters
A longer cycle can mean later ovulation, which may move the estimated due date later.
Planning around the date
Use the estimate for planning appointments, work, and support, then follow clinical guidance as pregnancy progresses.
Frequently asked questions
How do I calculate my due date?
Add 280 days, or 40 weeks, to the first day of your last menstrual period.
Is the due date exact?
No. It is an estimate, and many pregnancies deliver before or after that date.
What if I know my conception date?
Add about 266 days to conception for another due date estimate.
Can my doctor change my due date?
Yes. Ultrasound and clinical assessment can refine the estimate.