Due Date Calculator
Pregnancy due date and weekly milestones.
Estimated due date
Monday, June 28, 2027
280 days to go
Trimester milestones
A due date calculator estimates when a baby is likely to arrive, based on the first day of the last menstrual period or a known conception date.
Enter your last period date (or conception date) and the tool projects your estimated due date along with the trimester timeline and how many weeks along you are.
A due date is an estimate, not a deadline. Only a small share of babies arrive on the exact date; most come within a couple of weeks on either side.
How this calculator works
The standard method is Naegele's rule: pregnancy is counted as 280 days (40 weeks) from the first day of the last menstrual period (LMP), which assumes a regular 28-day cycle with ovulation around day 14. If you know your conception or ovulation date, the due date is about 266 days (38 weeks) from there. The calculator counts forward from the date you provide and marks the trimesters: the first runs through week 13, the second from weeks 14 to 27, and the third from week 28 to birth. A first-trimester ultrasound often refines the date, especially for irregular cycles.
What affects the number
- The LMP method assumes a regular 28-day cycle; longer or shorter cycles shift the estimate.
- A known conception or ovulation date gives a more precise due date than LMP alone.
- Early ultrasound dating is the most accurate and may adjust the estimate by days.
- Cycle irregularity is the most common reason an LMP-based date is off.
- First pregnancies more often go slightly past the due date than later ones.
- The due date is a midpoint; a normal, full-term arrival spans several weeks around it.
Frequently asked questions
How is a due date calculated?
The common method, Naegele's rule, adds 280 days (40 weeks) to the first day of your last menstrual period. If you know your conception date, the estimate is about 266 days from then. Both assume typical cycle timing, which an early ultrasound can refine.
How accurate is a due date?
It is an estimate. Only about 1 in 20 babies is born on the exact due date; most arrive within roughly two weeks before or after. Full term is considered 37 to 42 weeks, so a range is normal and expected.
Can I use conception date instead of my last period?
Yes. If you know your ovulation or conception date, counting about 38 weeks (266 days) forward gives the due date. This can be more accurate than the last-period method if your cycles are irregular.
What are the trimesters?
Pregnancy is divided into three trimesters: the first through week 13, the second from weeks 14 to 27, and the third from week 28 until birth. Each brings different developmental milestones, which the timeline in the calculator highlights.
This calculator provides general estimates for educational purposes only and is not financial, medical, legal, or tax advice. Your actual results depend on your specific situation and current rates.