About the due date
This calculator estimates your pregnancy due date from the first day of your last menstrual period and your average cycle length, using Naegele's rule. It also shows roughly how many weeks along you are. It runs in your browser; nothing is stored or uploaded.
How Due Date works
How to use it
- Enter the first day of your last period.
- Enter your average cycle length (28 days is typical).
- Read the estimated due date and how far along you are.
How it works
Naegele's rule adds 280 days (40 weeks) to the first day of the last period, adjusted for cycle lengths other than 28 days. Gestational age is counted from that first day, which is why it is about two weeks before conception.
Important
This is an estimate — only about 1 in 20 babies arrives on the exact due date. Always confirm with your doctor or midwife, who can refine the date with an ultrasound.
Common uses
- Estimate a pregnancy due date
- Find out how many weeks pregnant you are
- Plan around the due date
- Track gestational age
- Check the EDD from a last period
- Adjust for a longer or shorter cycle
- Understand pregnancy timing
- Prepare for appointments
Frequently asked questions
How is the due date calculated?
Last period + 280 days, adjusted for cycle length (Naegele’s rule).
Is my data uploaded?
No — it calculates in your browser and stores nothing.
Why count from my last period?
It is the most reliable known date; conception is about two weeks later.
What if my cycle is not 28 days?
Enter your length and the date is adjusted.
How accurate is it?
It is an estimate; few babies arrive on the exact date.
Should I rely on it medically?
No — confirm with your doctor or midwife.
Is it free?
Yes — completely free with no sign-up.