> ## Content Index
> Fetch the complete content index at: https://www.vizney.com/llms.txt
> Use this file to discover other available public pages before exploring further.

# Difference Between Standard Gregorian and ISO-8601
- URL: https://www.vizney.com/difference-between-standard-gregorian-and-iso-8601/
- Published: 2024-10-11T03:00:00.000Z
- Updated: 2024-10-12T02:43:41.000Z
- Description: This section explains the differences between the Standard Gregorian and the ISO-8601 Week-Based in date calculations.
- Author: Yehwan Hwang
- Tags: Knowledge Base

**ISO-8601** is an international standard for representing dates and times, designed to avoid confusion when exchanging data between countries with different conventions.

Here are the key differences between the Standard Gregorian and the ISO-8601 Week-Based:

#### Key Differences

![](https://storage.ghost.io/c/6a/50/6a50f03c-1922-4e90-bf18-c5abd0f819d4/content/images/2024/10/Week-start-day.png)

- The **Standard Gregorian** defines the week as starting on Sunday and ending on Saturday, while **ISO-8601** defines the week as running from Monday to Sunday.
- ISO-8601 does not use day names like "Sunday"; instead, Monday is represented as 1, Tuesday as 2, and Sunday as 7.
- ISO-8601 uses the format "W" followed by a two-digit number to represent the week (e.g., "W01" for the first week of the year).

![](https://storage.ghost.io/c/6a/50/6a50f03c-1922-4e90-bf18-c5abd0f819d4/content/images/2024/10/First-week-2025.png)

- In the **Standard Gregorian**, week numbers are reset based on January 1st, so **Week 53 of 2024** might only have 3 days, and **Week 1 of 2025** might have just 4 days.
- In **ISO-8601**, the first week of the year is the week that contains the **first Thursday**. For instance, in 2025, Week 1 starts on the week containing January 2nd. This means that **December 30th and 31st, 2024** are part of **ISO Week 1 of 2025**.

![](https://storage.ghost.io/c/6a/50/6a50f03c-1922-4e90-bf18-c5abd0f819d4/content/images/2024/10/First-week-2022.png)

- In the Standard Gregorian, **Week 1 of 2022** includes only January 1st. Under ISO-8601, however, Week 1 of 2022 starts on the week containing Thursday, January 6th, meaning **January 1st and 2nd, 2022** belong to **ISO Week 52 of 2021**.

#### Additional Resources

![](https://storage.ghost.io/c/6a/50/6a50f03c-1922-4e90-bf18-c5abd0f819d4/content/images/2024/10/Date-2022.png)

When using the **Standard Gregorian** to calculate week numbers, discrepancies can occur, especially for weeks at the beginning and end of the year where the number of days may differ. Be sure to pay special attention to these weeks.

Additionally, using functions like **DATEPART** or **DATERUNC** can result in different date inclusions, so it’s important to verify the output in your visualizations to ensure accuracy.

![](https://storage.ghost.io/c/6a/50/6a50f03c-1922-4e90-bf18-c5abd0f819d4/content/images/2024/10/Datepart---Datetrunc.jpg)