Counting Pregnancy Weeks: How to Read the Week of Pregnancy

How weeks of pregnancy are counted, what "12+3" means and when check-ups, ultrasound scans and maternity protection are due – as a guide.

Pregnancy3 linked calculatorsReading time: 5 min.

In Germany, weeks of pregnancy are counted from the first day of the last period. That is why you are already "in week 3" on paper when fertilisation has only just happened. Knowing the counting method makes the maternity record, check-up dates and deadlines easier to understand.

A guide, not a diagnosis

This information explains the counting method. How far along your pregnancy is will be determined by your doctor or midwife. If you have questions or symptoms, please contact your practice or midwife.

Key takeaways

  • In the maternity record, pregnancy is counted from the first day of the last period: 40 weeks or 280 days.
  • Counted from fertilisation, it is 38 weeks or 266 days – so the baby is about two weeks younger than the week of pregnancy suggests.
  • "12+3" means 12 completed weeks and 3 days. That is the 13th week of pregnancy.
  • The Maternity Guideline generally provides for check-ups every four weeks, and two per month in the last two months.
  • Maternity protection starts six weeks before the estimated due date, i.e. at 34+0 by calculation.

Two ways of counting: from the period and from fertilisation

At the first check-up, the maternity record (Mutterpass) is issued and the first day of the last period is entered as the start of pregnancy. Counted this way, a pregnancy lasts 40 weeks or 280 days. The Maternity Guideline also uses this "post menstruationem" (p.m.) method.

Fertilisation usually takes place about two weeks later. Counted from fertilisation, pregnancy lasts 38 weeks or 266 days, and the weeks match the age of the baby. At the end of week 12 according to the maternity record, the baby is therefore about ten weeks old.

Calculate your week of pregnancy

Week and day of pregnancy from the first day of the last period.

Calculate now

What "12+3" means

The maternity record and medical findings usually give the length of pregnancy as completed weeks plus days: "12+3" means 12 full weeks and 3 days. At the same time this is called the 13th week of pregnancy, because week 13 is in progress. The Maternity Guideline, for example, gives the ultrasound scans in both notations:

Week of pregnancyNotation in the maternity recordPurpose under the Maternity Guideline
weeks 9 to 128+0 – 11+61st routine ultrasound
weeks 19 to 2218+0 – 21+62nd routine ultrasound
weeks 29 to 3228+0 – 31+63rd routine ultrasound

Periods according to section 2(9) of the Maternity Guideline (8+0 to 11+6, 18+0 to 21+6, 28+0 to 31+6 weeks) and the patient information in Annex V (weeks 9 to 12, 19 to 22, 29 to 32).

Maternity protection and due date in weeks

An example with a made-up date: if the last period started on January 4, 2027, the estimated due date is October 11, 2027. In weeks of pregnancy, that means:

  • Start of the protection period before delivery, six weeks before the due date (section 3(1) MuSchG): week 34+0
  • Estimated due date: week 40+0

Calculated with our pregnancy week and maternity protection calculators.

Calculate maternity protection

Start and end of the protection periods from the due date.

Calculate now

Check-ups during pregnancy

Under the Maternity Guideline, check-ups should generally take place every four weeks, regardless of symptoms; in the last two months of pregnancy, two check-ups per month are generally indicated (section 2(8)). Your practice will discuss which appointments suit you.

Calculate the due date

Estimated due date from the first day of the last period.

Calculate now

Frequently asked questions

What does 12+3 weeks mean?
12 completed weeks and 3 days since the first day of the last period. You are therefore in the 13th week of pregnancy.
When does pregnancy start counting?
In the maternity record, from the first day of the last period, even though fertilisation usually happens about two weeks later.
How many weeks does a pregnancy last?
Counted from the last period, 40 weeks (280 days); from fertilisation, 38 weeks (266 days). Babies are rarely born on exactly the estimated due date.
In which week does maternity protection start?
Six weeks before the expected date of delivery (section 3(1) MuSchG). If the due date is at 40+0, that is 34+0 by calculation.

Sources

Every figure in this article comes from these primary sources or from the linked calculators, which are based on the same sources.

  1. familienplanung.de (Federal Institute for Public Health, BIÖG): how pregnancy weeks are counted (accessed September 30, 2026)
  2. Federal Joint Committee (G-BA): Maternity Guideline (section 1(8), section 2(8) and (9)) (accessed September 30, 2026)
  3. Maternity Protection Act (MuSchG), section 3 (protection periods) (accessed September 30, 2026)
Onur Cirakoglu — Full-Stack Developer & Founder of HEADON.pro
Onur CirakogluSources verified

Full-Stack Developer & Founder of HEADON.pro

Full-stack developer and founder of HEADON.pro. Developer of Rechnerzentrale.