Pregnancy Due Date Calculator: When Will I Give Birth?

Medical review: Dr. Sheila Sedicias
Gynecologist
July 2022

A due date is the day which commemorates 40 weeks of pregnancy, counting back from the first day of the last period. 

The easier way to calculate the due date is to add 7 days and 9 months to the first day of the last period. For example, if your last period started on August 12, then add 7 days and 9 months, which will bring you to May 19. 

You can also use our online calculator to determine your due date: 

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This day is just a guide for the women and her doctor, as the baby may not be born on this exact date. The baby may be born before or after this date. 

How to calculate due date from ultrasound 

Ultrasound is the most accurate way of determining a due date, as the technologist can visualize certain growth parameters and compare them to the average fetal growth markers of other babies. With this information, the doctor can predict the due date with greater accuracy. 

Even though it is more precise, this due date can still be changed, as the birth will be determined by the baby and the mother’s body, especially if a vaginal birth is imminent.

How to calculate due date from conception date

If you are certain of the conception day, you can add 280 days to the day and divide this by 7 (for 7 days of the week). This result will give you the probably weeks with which the baby will be born, which you can then check on the calendar. 

For example, if you conception date was August 12, add 12 + 280 days and then divide by 7. This will give you 41 weeks. Look for August 12 on the calendar and then add 41 weeks. This means the baby will likely be born on May 19. 

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Atualizado por Tua Saude editing team, em July de 2022. Medical review por Dr. Sheila Sedicias - Gynecologist, em May de 2022.

References

  • STATPEARLS. Estimated Date of Delivery . Available on: <https://www.ncbi.nlm.nih.gov/books/NBK536986/>. Access in 03 Sep 2020
  • HUM REPROD. Length of human pregnancy and contributors to its natural variation. 2013. Available on: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3777570/>. Access in 03 Sep 2020
Show more references
  • STATPEARLS. Pregnancy Dating. 2020. Available on: <https://www.ncbi.nlm.nih.gov/books/NBK442018/>. Access in 03 Sep 2020
  • FEDERAÇÃO BRASILEIRA DAS ASSOCIAÇÕES DE GINECOLOGIA E OBSTETRÍCIA. MANUAL DE ASSISTÊNCIA PRÉ-NATAL. Available on: <https://www.febrasgo.org.br/images/arquivos/manuais/Manuais_Novos/Manual_Pre_natal_25SET.pdf>. Access in 03 Sep 2020
Medical review:
Dr. Sheila Sedicias
Gynecologist
Physician graduated in Mastology and Gynecology by UFPE in 2008 and member no. 17459 of CRM-PE, Brazil.