Due Date Calculator
This calculator is currently available in English only. Open the English page →
Your estimated due date is 280 days, or 40 weeks, after the first day of your last period. Enter that date below to see your due date, or enter a due date you already have to see how many weeks pregnant you are today.
Enter a date to see your estimated due date and how many weeks pregnant you are today.
Worked out from today's date on your device. An estimate for reference only: your midwife or doctor confirms your due date.
Medical disclaimer: BabyBerry 提供的内容仅用于一般信息和自我记录，不是医疗器械，也不构成医疗建议、诊断或治疗。请始终向具备资质的医疗人员咨询。
How the due date is worked out
Pregnancy weeks are counted from the first day of your last period, not from conception, which usually happens about two weeks later. That is why you are already counted as a few weeks pregnant by the time a test turns positive.
The calculator adds 280 days to that date. Doing it by hand gives nearly the same answer: add one year, subtract three months and add seven days (Naegele's rule). Both assume a cycle of about 28 days.
BabyBerry's app uses the same 280-day count, so the week you see here is the week the app shows.
Why your provider's date may be different
If your cycles are usually longer or shorter than 28 days, or you are not sure when your last period started, a date from your period alone can be off by days or weeks.
The American College of Obstetricians and Gynecologists (ACOG) recommends that the due date be set from your last period, an early ultrasound, or both, and that it be confirmed or revised by an ultrasound before 22 weeks. Once set, it should change only in rare circumstances.
If your midwife or doctor has given you a due date, use theirs: choose "A due date I already have" above.
A due date is a window, not a day
Your due date marks 40 weeks. ACOG describes births by the week they happen in:
- Early term: 37 weeks 0 days to 38 weeks 6 days
- Full term: 39 weeks 0 days to 40 weeks 6 days
- Late term: 41 weeks 0 days to 41 weeks 6 days
- Postterm: 42 weeks 0 days and later
Trimesters
BabyBerry counts weeks 1 to 12 as the first trimester, weeks 13 to 27 as the second and week 28 onward as the third. Some providers and guides draw the lines a week earlier or later.
Due date questions
How is a due date calculated?
By adding 280 days (40 weeks) to the first day of your last period. It assumes a cycle of about 28 days, so your midwife or doctor may set a different date, usually after an early ultrasound.
How many weeks pregnant am I?
Count the weeks since the first day of your last period. Enter that date above, or enter the due date you were given, and the calculator shows your weeks and days as of today.
Can my due date change?
It can be revised once an early ultrasound has been done. ACOG recommends the due date be confirmed or revised by an ultrasound before 22 weeks, and changed after that only in rare circumstances.
What if I don't know when my last period started?
Your midwife or doctor can date the pregnancy with an ultrasound. Until then, an approximate date gives a rough idea only.
Will my baby arrive on the due date?
The due date marks 40 weeks, but births from 37 weeks 0 days through 41 weeks 6 days are all classed as term by ACOG, so arriving on a different day within that window is normal.
Sources
This page is general information for reference, written by the BabyBerry team from public guidance: