Week Number Calculator · Current Week Number｜Annual Week Statistics
Accurately calculate the week number of any date within the year. Supports custom week start rules (Monday/Sunday), displays current week range, total weeks in the year. Pure local computation, privacy safe.
* ISO Rule: Week containing the first Thursday is week 1; US Rule: Week containing Jan 1 is week 1
Week Details · Period Analysis
👈 Please select a date and click calculate
Supports custom dates and week start rules, quickly get week number, week range, total weeks in year
Week Number Calculator - Complete User Guide & Features
📌 What is the Week Number Calculator?
The Week Number Calculator is an online tool that helps you quickly find out which week of the year any given date falls into. Whether you are planning projects, scheduling semesters, tracking workouts, or need to know the current week number, this tool provides accurate answers.
- Check current week number —— The page automatically displays the week number for today's date without any manual action.
- Custom date query —— Supports selecting any date (Gregorian calendar), easily review or predict the week number for any date.
- Dual rule support —— Provides ISO international standard (Monday as first day of week) and US rule (Sunday as first day of week), meeting different regional and usage habits.
- Current week start and end dates —— Displays the start day (Monday or Sunday) and end day of the week for the selected date, convenient for weekly planning.
- Total weeks in the year statistics —— Automatically calculates the total number of weeks in the selected year (52 or 53 weeks).
- Remaining weeks & Next week number —— Quickly understand how many weeks are left from the current week to the end of the year, and the week number of the following week.
📐 Calculation Principles & Formulas
I. How to calculate the week number for a given date?
The core idea for calculating the week number of a date is: Find the start date of the first week of the year, then calculate how many complete 7-day cycles have passed between the target date and that start date.
The key lies in defining the "first week start date", which depends on your chosen week start rule:
· ISO Standard (Monday start): The first week is the week containing the first Thursday of the year. The Monday of that week is the first week start date.
· US Rule (Sunday start): The week containing January 1st is the first week. The Sunday of that week is the first week start date.
II. How to determine how many weeks are in a year?
The total number of weeks in a year depends on whether the last week crosses into the next year and the chosen week start rule. Generally, a year has 52 or 53 weeks.
ISO Standard: If January 1st is a Thursday, or if it's a leap year and January 1st is a Wednesday, then the year has 53 weeks.
US Rule: If January 1st is a Sunday, or if it's a leap year and January 1st is a Saturday, then the year has 53 weeks.
III. How to calculate the current week's start and end dates?
Once the first day of the week (Monday or Sunday) is determined, calculating the current week's range is straightforward:
For example, using the ISO standard (Monday=1, Sunday=7): If today is Wednesday (value=3), the current week's Monday is today minus 2 days; the current week's Sunday is that Monday plus 6 days.
IV. Application Scenarios for Week Number Calculation
Project Management & Work Planning: Many businesses plan work, hold weekly meetings, and submit weekly reports based on weeks.
Education & Teaching: Schools typically schedule courses and exams by semester and week number. Teachers and students need to know the current teaching week.
Fitness Tracking & Habit Formation: Track workouts and habits on a weekly cycle; knowing the week number helps with review and planning.
Financial Reporting & Payroll: Some companies calculate payroll or compile financial data on a weekly basis.
Software Development & Iteration: Agile development often uses weeks to plan Sprint cycles.
📝 Usage Steps
- Select Date Mode —— Default "Today's Date" displays the current week number; Click "Custom Date" to manually select any date.
- Set Week Start Rule —— Choose "Monday as first day of week (ISO Standard)" or "Sunday as first day of week (US)" based on your needs.
- Click Calculate Week Info —— Instantly displays the week of the year, current week start/end dates, total weeks in the year, and other supplementary information.
- Modify any options —— Recalculate to update results in real-time.
⚠️ Important Notes
- ISO Week Standard: The first week of the year must contain January 4th or the first Thursday, so January 1st might belong to the last week of the previous year.
- Cross-Year Week Handling: A date at the end of the year (e.g., December 31st) might belong to the first week of the next year. This tool correctly displays the week number's year affiliation.
- Privacy Protection: This tool is pure front-end implementation. All calculations are performed locally in your browser, and no personal information is uploaded to any server.
- Date Range: This tool supports dates between year 1000 and 9999, fully meeting daily usage needs.
- Leap Year February 29: This tool correctly handles leap year dates and will not have calculation errors for February 29th.