Calculating the Due Date: How the Estimated Date Is Worked Out

The rule: 280 days from the last period

Because the day of fertilisation is usually unknown, the calculation starts from the first day of the last period. It is 280 days, i.e. 40 weeks, to the estimated due date. This is also how the length of pregnancy is counted in the German maternity record.

Fertilisation usually takes place about two weeks after the start of the last period. From fertilisation to birth, a pregnancy therefore lasts 266 days or 38 weeks on average.

If you wish, our calculator takes a different cycle length into account: it shifts the date by the number of days your cycle is longer or shorter than 28 days. This is a simplifying assumption; the date your practice or midwife enters is what counts.

Examples

Three worked examples with made-up dates:

Calculated with our due date calculator. Under the assumption above, a cycle length of 32 days shifts the date by 4 days.

Ultrasound and reality

The Maternity Guideline provides for three routine ultrasound scans, the first in weeks 9 to 12 of pregnancy. Its measurements help to estimate the week of pregnancy and the expected date of delivery. If the result differs from the calculation, the practice may adjust the date.

Even a carefully determined date remains an estimate: the estimated due date is rarely the child's actual birthday.

Which date counts for the maternity record and maternity protection

For the protection period before delivery, the expected date of delivery as stated in the certificate from a doctor or midwife is decisive (section 3(1) MuSchG). This certificate should contain the expected date of delivery; your employer may ask for it (section 15(2) MuSchG). If the baby arrives earlier or later, the protection period before the birth becomes shorter or longer accordingly.

Frequently asked questions