Convert any calendar date to its corresponding ISO 8601 week number and year instantly. Perfect for developers, accountants, planners, and data analysts, this free online tool ensures consistent week-based date representation for reporting, project management, payroll, and software systems.
🧭 What is an ISO Week Date?
The ISO week date is part of the ISO 8601 international standard. Key rules:
- Weeks start on Monday.
- Week 1 is the week containing the first Thursday of the year (January 4th).
- ISO weeks are numbered from 1 to 52 or 53, depending on the year.
Example:
- 2025-01-01 → 2025-W01-3 (Wednesday)
- 2025-12-31 → 2025-W53-3
This format is widely used in international business calendars, ERP systems, financial reporting, and software development.
⚙️ How the ISO Week Date Converter Works
- Enter a date in standard format (YYYY-MM-DD).
- The tool automatically calculates:
- ISO Week Year
- ISO Week Number
- ISO Weekday (1 = Monday … 7 = Sunday)
- Results are displayed in ISO format: e.g., 2025-10-28 → 2025-W44-2.
You can use it to convert Gregorian dates, generate ISO week calendars, or cross-check week numbers for reporting and software tasks.
🧩 Why Use an ISO Week Converter?
- 🗓️ International Standardization – Avoid confusion between different country date systems.
- 📊 Reporting & Data Systems – Weekly reports, analytics, and financial summaries.
- 💻 Developer-Friendly – Convert dates for APIs, databases, and scheduling algorithms.
- 🕒 Project Management – Align tasks and schedules precisely with ISO weeks.
- 🧮 Instant & Accurate – No manual calculations required.
🌐 Use Cases
- Business Reporting – Generate weekly sales or revenue reports.
- Payroll Management – Track payments or attendance by ISO week.
- Software Development – Convert dates for backend systems.
- Academic Planning – Align schedules with ISO week calendars.
- Manufacturing & Logistics – Plan weekly production and shipping cycles.
🔢 Key Features
- ✅ Instant date-to-week conversion.
- ✅ Supports all years and leap years, fully ISO 8601 compliant.
- ✅ Displays ISO weekday (Monday = 1 … Sunday = 7).
- ✅ User-friendly interface, clear output.
- ✅ Free and web-based, no registration required.
- ✅ Cross-browser compatible, works on desktop and mobile.
📘 Example Conversions
| Calendar Date |
ISO Week Date |
Description |
| 2025-01-01 |
2025-W01-3 |
Wednesday, Week 1 of 2025 |
| 2025-06-30 |
2025-W27-1 |
Monday, Week 27 |
| 2025-12-31 |
2025-W53-3 |
Wednesday, Week 53 |
| 2024-12-30 |
2025-W01-1 |
Monday, first week of 2025 |
💼 Benefits of Using AlllinTools.com ISO Week Converter
- 🌍 Global compatibility with ISO 8601 standard.
- 📅 Accurate week-year representation, handles year transitions.
- 💾 Developer-friendly for exporting or scripting.
- 🔄 Multi-purpose use for business, development, or analytics.
- 🔐 Privacy-safe, input stays local to your browser.
💡 FAQs
- What is an ISO Week Date Converter? – Converts any date to ISO week number and ISO year.
- What is ISO 8601? – International standard for dates, times, and week numbering.
- Why do some years have 53 weeks? – If the year starts/ends near Thursday.
- What does “W” mean? – “Week,” e.g., 2025-W44-2 = Tuesday of 44th week.
- Can I convert multiple dates? – Yes, via repeated entries or automated scripts.
- Difference between ISO week year and calendar year? – ISO week year may differ around new year transitions.
- Is it free? – Yes, completely free online.
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🏁 Conclusion
The ISO Week Date Converter is a simple, accurate tool for converting calendar dates to ISO 8601 week format. Ideal for developers, analysts, accountants, and business professionals who rely on week-based data for reporting, payroll, and scheduling. Get instant, standardized, and precise results every time with AlllinTools.com.