Due Date Calculator
Calculate the expected due date of your baby using Naegele's rule. With clear explanations, recommendations and comparison values.
Note: These calculations are for informational purposes only and do not replace professional tax or financial advice. All information without guarantee.
FAQ
Frequently Asked Questions
How is the due date calculated?
The due date is calculated using Naegele's rule: first day of last period plus 7 days minus 3 months plus 1 year. The standard pregnancy duration is 280 days (40 weeks) from the last menstrual period.
How accurate is the calculated due date?
Only about 4% of babies are born on their calculated due date. About 90% are born within two weeks before or after. Ultrasound dating in the first trimester is the most accurate method.
Does this calculator replace a doctor visit?
No. This calculator provides general orientation only. For medical questions, or before starting a diet, therapy or treatment, always consult a qualified physician or therapist.
Guide
Quick Answer
The due date calculator computes the expected delivery date based on the first day of the last menstrual period or the conception date.
What is the Due Date Calculator?
The due date calculator computes the expected delivery date based on the first day of the last menstrual period or the conception date.
How does the Due Date Calculator work?
Enter the first day of your last period. Using Naegele's rule: due date = first day of last period + 7 days - 3 months + 1 year. With a known conception date: due date = conception + 266 days. The current pregnancy week is also shown.
Key Data and Facts
Naegele's rule: last period start + 7 days - 3 months + 1 year. Pregnancy duration: 280 days = 40 weeks. Only about 4% of babies are born on the calculated date.
Step-by-Step Guide
How to calculate the due date step by step: 1. Enter the first day of your last menstrual period: this date is the basis of Naegele's rule. 2. Apply Naegele's rule: due date = first day of the last period + 7 days - 3 months + 1 year. Alternatively: due date = first day of the last period + 280 days. 3. If the date of conception is known: due date = date of conception + 266 days (38 weeks). 4. Read off the current week of pregnancy: the calculator shows the current week of pregnancy (SSW) and the exact day of pregnancy. Example: SSW 12+3 means the 12th week and 3 days. 5. Trimester division: 1st trimester SSW 1-12, 2nd trimester SSW 13-27, 3rd trimester SSW 28-40. 6. Note: only about 4 % of babies are born on the calculated due date. Most births take place between SSW 38 and SSW 42. The gynaecologist can refine the date with an ultrasound measurement.
Calculation Example
Last period: January 15, 2026. Due date by Naegele: 15 + 7 = 22, January - 3 months = October, + 1 year: October 22, 2026. Pregnancy duration: 280 days.
Sources · E-E-A-T
Official sources
Calculations are based on applicable German laws and official data:
Full methodology at Methodology.
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