This calculator determines the week number of the year for a given date. This can be useful for planning, scheduling, and tracking purposes.

使い方：

• Select a date using the date picker.
• Click the "計算する Week 数値" button.
• The week number will be displayed in the results section.

How it Works:

The calculator determines the day of the year (from 1 to 365 or 366) and then divides that number by 7. The result is rounded up to the nearest whole number to give you the week of the year.