Pregnancy week calculator

Calcolo Settimane di Gravidanza

Use the Mamma in Progress online calculator above to determine which week of pregnancy you are in:

Enter the start date of your last menstrual cycle and click on the ‘Calculate Pregnancy Week’ button to display the result.

How to Calculate Pregnancy Weeks

Pregnancy weeks are commonly calculated using a woman’s last menstrual cycle date. Here’s how the calculation works:

  1. Last Menstrual Cycle Date: The woman provides the start date of her last menstrual cycle.
  2. Determination of Current Date: The current date is determined, which is when the calculation is being done.
  3. Calculation of Pregnancy Days: The difference between the current date and the last menstrual cycle date is calculated. This gives us the total number of pregnancy days.
  4. Conversion into Weeks: The total pregnancy days are divided by 7 since there are 7 days in a week. The result gives us the number of pregnancy weeks.

For example, if the last menstrual cycle date is January 1, 2024, and the current date is March 1, 2024:

  • The difference in days is 59 days.
  • Dividing 59 days by 7, we get approximately 8 weeks of pregnancy.

This is a basic calculation to estimate pregnancy weeks. However, it’s important to note that every pregnancy is unique, and precise calculation may require additional considerations, especially in the early stages of pregnancy. Additionally, prenatal ultrasounds can be used to confirm gestational age more accurately.

Pregnancy Trimesters

During pregnancy, trimesters are divided into approximately three-month periods and serve to provide a framework for understanding fetal changes and development, as well as changes in the mother’s body. Here’s a brief overview of pregnancy trimesters:

  • First Trimester (Weeks 1-12) Approximate Duration: 0-3 months of pregnancy.
  • Second Trimester (Weeks 13-26) Approximate Duration: 4-6 months of pregnancy.
  • Third Trimester (Weeks 27-40+) Approximate Duration: 7-9 months of pregnancy until delivery.

It’s important to keep in mind that these trimester divisions are approximate and vary from woman to woman. Additionally, the exact timing of when a woman enters each trimester may vary slightly depending on her menstrual cycle and individual fetal development.

Pregnancy Weeks and Corresponding Months

Pregnancy weeks do not exactly correspond to calendar months, as a month can vary in length from 28 to 31 days. However, for an approximate indication, we can make an estimation.

Typically, pregnancy is considered to last 40 weeks (or 280 days) from the date of the last menstrual cycle. Here’s an approximate correspondence between pregnancy weeks and calendar months:

1st Trimester: 1-12 weeks

This encompasses approximately the first 3 months of pregnancy.

2nd Trimester: 13-26 weeks

This encompasses approximately the 4th, 5th, and 6th months of pregnancy.

3rd Trimester: 27-40+ weeks

This encompasses the remainder of pregnancy until delivery, including part of the 7th, 8th, and 9th months.

Keep in mind that this correspondence is approximate and may vary slightly depending on how weeks and months are calculated in a given context. Additionally, the actual duration of pregnancy can vary from woman to woman.


Here’s an approximate table showing the correspondence between months and weeks of pregnancy:

Month of PregnancyWeeks of Pregnancy (Approximate)
1° month1-4 weeks
2° month5-8 weeks
3° month9-13 weeks
4° month14-17 weeks
5° month18-21 weeks
6° month22-26 weeks
7° month27-30 weeks
8° month31-35 weeks
9° month36-40+ weeks

Please note that this table provides only an approximate estimation. Every pregnancy is unique, and the actual duration of each trimester and month may vary from woman to woman. Always consult your doctor for specific information about your pregnancy.

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