Master Your Time with the Ultimate Week Calculator
Time is more than just hours and minutes; for businesses and planners worldwide, it's measured in weeks. Whether you're tracking a pregnancy, managing a project sprint, or scheduling a supply chain delivery, knowing the exact week number is indistinguishable from success.
Did you know? Most of the world uses the ISO 8601 standard, where weeks start on Monday. The US system often starts on Sunday. Our tool is built for precision, adhering to global ISO standards to prevent costly scheduling mix-ups.
Key Features of This Tool
We've designed this calculator to be your "Swiss Army Knife" for date planning. Here is what makes it special:
Instant Week Lookup
Enter any date from the past or future to instantly get its exact ISO Week Number and Year.
Reverse Calculation
Have a week number (e.g., "Week 42")? We'll tell you exactly when it starts (Monday) and ends (Sunday).
Date Arithmetic
Need to know the date 10 weeks from today? Or what date was 6 weeks ago? Our "Add/Sub" tab does the math.
Live Progress
Our hero widget shows you the current week in real-time and visualizes how much of the year has passed.
How to Use the Week Calculator
Follow these simple steps to get the answers you need:
1. To Find a Week Number
- Click the "Find Week" tab (active by default).
- Select your target date using the date picker.
- The result will instantly appear, showing the Week Number (e.g., Week 01) and the correct ISO Year. Note that dates in late December can sometimes belong to the next year's Week 1!
2. To Find Dates from a Week Number
- Switch to the "Week to Date" tab.
- Enter the Year (e.g., 2024) and the Week Number (1-53).
- Click "Find Dates".
- The tool will display the Start Date (Monday) and End Date (Sunday) for that specific week.
3. To Add or Subtract Weeks
- Switch to the "Add/Sub" tab.
- Choose a Start Date (defaults to today).
- Select "Add (+)" or "Subtract (-)".
- Enter the number of weeks (e.g., 6 for a standard maternity leave or project phase).
- The calculates future or past date will appear instantly.
Deep Dive: ISO 8601 Logic Explained
Why is this calculator necessary? Because the calendar is messy. The ISO 8601 standard was created to fix this by defining a standardized "Week Date" system used by governments and multinationals.
- The Monday Rule: Weeks always start on Monday and end on Sunday.
- The First Thursday Rule: Week 1 of any year is the week that contains the first Thursday of January. Equivalently, it is the week that contains January 4th.
- The 52/53 Week Rule: Most years have 52 weeks. However, if a year starts on a Thursday (or is a leap year starting on Wednesday), it gets a 53rd week. This keeps the calendar in sync with the solar year.
This logic handles tricky edge cases. For instance, January 1, 2027 is a Friday. Under ISO rules, it is actually part of Week 53 of 2026, not Week 1 of 2027! Our calculator handles these complexities so you don't have to.
❓ Frequently Asked Questions
Does the US use ISO week numbers?
Not usually. The US system typically starts weeks on Sunday, and Week 1 is the week containing Jan 1st. This can lead to significant differences. Our tool adheres to the international ISO standard used by most other countries and multinational businesses.
Can a week number be 53?
Yes! Approximately every 5-6 years, a year has 53 weeks. This happens to account for the fact that 52 weeks * 7 days = 364 days, leaving 1 extra day (or 2 in leap years) that eventually stacks up to a full extra week.
Is this tool free to use for commercial planning?
Absolutely. This tool is free, accurate, and available 24/7 for all your business and personal scheduling needs.