Use a browser-based ISO week number calculator: it shows the current week number, or the week number for any date you enter, using the ISO 8601 standard, along with the week year and the range of dates that week covers. It runs on your device and settles the common disagreements about which week it is.
Asking what week of the year it is has more than one answer unless you fix a standard. The ISO 8601 rule, which most of the world of business and software uses, says weeks start on Monday and week 1 is the week containing the first Thursday of the year. That can put early January into the last week of the previous year, or late December into week 1 of the next, which is why a calculator that follows the standard is worth using.
A good week number tool gives you more than a single number: the ISO week, the week year it belongs to, the day of the week, and the start and end dates the week spans. That matters for planning and reporting, where fiscal calendars, sprint numbering and scheduling all lean on ISO weeks. The calculation runs in your browser, so a date you check is never sent to a server.
ISO 8601, where weeks start on Monday and week 1 is the week containing the first Thursday of the year.
Under ISO rules a week belongs to the year that holds most of it, so the first days of January can fall in the previous week year.
No. The calculation runs entirely in your browser.