Tool · Calculator
Pregnancy Calculator: Estimate Due Date & Gestational Week
Enter the first day of your last period or your due date. The calculator instantly shows your current gestational week, the trimester and a realistic birth window — no “calculate” button needed.
Gestational age is counted from this day.
Shifts the due date only, never the gestational week.
Enter a date and the tool calculates right away.
A note on accuracy
The result is an estimate and does not replace medical advice. Your doctor or midwife determines the exact date by ultrasound.
What the calculator does
Calculates as you type
Enter a date and the result is there — no button, no waiting.
Two ways in
Start from your last period, or from a due date your practice already gave you.
Your own cycle length
20 to 45 days. It shifts the due date; the gestational week stays tied to the LMP.
A window, not a deadline
Shows how births realistically spread around the estimated due date.
Check-ups and deadlines
Ultrasounds, glucose test, anti-D and the maternity leave dates, all with real dates.
Export as .ics
Load every upcoming appointment into your own calendar with one click.
The three trimesters
Week 1–13
All organs form. The due date is confirmed by ultrasound.
Week 14–27
Growth phase with the anomaly scan and the gestational diabetes test.
from week 28
Check-ups every two weeks; maternity leave starts six weeks before the due date.
The terms in short
- Gestational week
- Counted from the first day of your last period — not from conception.
- 40+3
- Completed weeks plus days. “40+3” means 40 weeks and 3 days have passed; you are in week 41.
- LMP
- Last menstrual period, the first day of your last period. Day 1 of the whole count.
- EDD
- Estimated due date, 280 days after the LMP. A probability, not a fixed date.
- Naegele's rule
- The rule behind it: first day of the last period plus 280 days, adjusted for cycle length.
- Maternity leave
- Six weeks before the due date until eight weeks after birth; twelve for premature and multiple births.
How this pregnancy calculator works
This pregnancy calculator primarily uses the established Naegele's rule. It starts from the first day of your last menstrual period (LMP) and adds 280 days, which equals 40 weeks of gestation or the average length of a pregnancy. That gives the estimated due date (EDD).
For a more precise estimate, especially if your cycle length differs from the average of 28 days, the calculator also takes your individual cycle length into account. That value adjusts the due date. The current gestational week, however, is always counted from the first day of your last period.
If your practice has already given you a due date, the tool works backwards: it subtracts 280 days and derives the start of the count and your current gestational week from there.
Understanding your pregnancy calculation
Estimated conception date
Besides the due date, the calculator also estimates the likely date of conception. In a 28-day cycle it falls roughly 14 days after the first day of the last period, usually around ovulation. The tool adjusts this to your cycle length.
What does gestational week mean?
The gestational week indicates how far the pregnancy has progressed. Week 1 starts on the first day of your last period, even though conception usually happens about two weeks later. A full-term pregnancy lasts about 40 weeks, or 280 days.
Why a birth window instead of a single day?
Very few babies arrive exactly on the estimated due date. Around 60 percent are born by then, another 35 percent in the two weeks after, and about 5 percent later. That is why the calculator shows a window with concrete dates rather than one day.
Check-ups and maternity leave
The windows for ultrasounds, the glucose tolerance test and anti-D prophylaxis follow the German maternity guidelines; the maternity leave deadlines follow the German Maternity Protection Act: work is not permitted from six weeks before the estimated due date, and the leave ends no earlier than eight weeks after birth. Your practice always sets the exact appointment.
Always consult your doctor or midwife
While this calculator is a helpful tool for orientation, it does not replace professional medical advice. Discuss the calculated dates and your pregnancy with your doctor or midwife. They can give accurate information through check-ups and ultrasounds, monitor your baby's development and support you throughout the pregnancy, including topics such as maternity protection.
Frequently asked questions
- How do I work out my current gestational week?
- The gestational week is counted from the first day of your last period, not from conception. Divide the days between the LMP and today by seven to get the completed weeks; the running week is one higher. The calculator does this for you and also shows the “weeks+days” notation, for example 22+4.
- What does 40+3 mean?
- It stands for 40 completed weeks plus three days, counted from the first day of the last period. In gestational-week terms you are in week 41.
- Does my cycle length change the gestational week?
- No. Cycle length only shifts the estimated due date, because ovulation happens later in longer cycles. The gestational week is always counted from the first day of the last period and stays unaffected.
- How accurate is the estimated due date?
- It is an estimate. About 60 percent of babies arrive by the estimated due date, another 35 percent within the two weeks after, and around 5 percent after week 42. A first-trimester ultrasound gives a more precise dating.
- When does maternity leave start in Germany?
- Maternity leave starts six weeks before the estimated due date and ends no earlier than eight weeks after birth. For premature births, multiple births and children with disabilities the period after birth extends to twelve weeks.
- Can I add the dates to my calendar?
- Yes. The calculator generates an .ics file containing every upcoming screening window and deadline. It imports into Apple Calendar, Google Calendar, Outlook and any other calendar app.
- Is my data stored anywhere?
- Your input stays in the browser. Date, mode and cycle length are saved locally so they are still there on your next visit. Nothing is sent to a server.