Due Date Calculator
From the first day of your last period, get the due date by Naegele's rule plus the current pregnancy week, trimester, days remaining and key milestone dates.
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
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, or choose "Conception" if the date of conception is known for certain. Using Naegele's rule: due date = first day of last period + 7 days - 3 months + 1 year (= + 280 days). With a known conception date: due date = conception + 266 days. The current pregnancy week is shown in completed weeks + days (e.g. 36+2 = week 37).
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 (option "Conception"): due date = date of conception + 266 days (38 weeks); the pregnancy week is still counted from the calculated last period (conception - 14 days). 4. Read off the current week of pregnancy: the calculator shows the completed weeks and days since the first day of the last period. Example: 12+3 means 12 completed weeks and 3 days – you are in week 13 of pregnancy. 5. Trimester division (in completed weeks + days): 1st trimester up to 12+6, 2nd trimester 13+0 to 27+6, 3rd trimester from 28+0 until birth. 6. Note: only about 4 % of babies are born on the calculated due date. Most births take place between week 38 and week 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. Status on 26 September 2026: 254 days have passed since 15 January = 36 completed weeks + 2 days (36+2), i.e. week 37 of pregnancy in the 3rd trimester; 26 days remain until the due date. With a known conception date of 29 January 2026: 29 January + 266 days = also 22 October 2026.
Sources
Official sources
Calculations are based on applicable German laws and official data:
Full methodology at Methodology.
Reviewed by Konstantin Iakovlev · Last updated:
Health
Related Calculators
BMI Calculator
Enter your height and weight to get your body mass index and its WHO category: underweight, normal weight, overweight or obese.
Calorie Calculator
Get your basal metabolic rate (Mifflin-St Jeor) and daily calorie needs by activity level from age, height, weight and sex, plus targets to lose or gain weight.
Ovulation Calculator
Enter the first day of your last period and your cycle length to see the estimated ovulation date, fertile days and next period, also on a monthly calendar.
Pregnancy Week Calculator
Find your pregnancy week from your last period or due date, with trimester, days remaining, the baby's development stage and estimated size and weight.