How to use (3 steps)
- Select a date (use “Today” for a one-tap reset).
- Choose the week rule (ISO or simple with Mon/Sun start) and set the fiscal year start month plus label mode.
- Review the week range, calendar quarter, fiscal quarter/year, then copy results or a shareable link.
UTC-based date math avoids time zone shifts. Week 1 definitions are shown below the inputs.
Inputs
Results
ISO week
- Week—
- Week-year—
- Weekday—
- Range—
Simple week
- Week—
- Year—
- Start day—
- Range—
Fiscal year details
- Label—
- Range—
- Quarter—
Date details
- Day of year—
- Days left (year)—
- Weeks left (year)—
- Days left (fiscal year)—
- Weeks left (fiscal year)—
How it’s calculated
- ISO weeks start on Monday; Week 1 is the week containing Jan 4 (first Thursday). Week-year may differ from the calendar year.
- Simple weeks use the start day you choose; Week 1 is the week containing Jan 1.
- Calendar quarter = floor((month−1)/3)+1.
- Fiscal year starts on the month you set; label can be start year or end year. Fiscal quarters advance every 3 months from that start.
- Day of year counts from Jan 1 (1–365/366), using UTC.
- Days/weeks left are counted to Dec 31 (calendar year) and to your fiscal year end date (excluding the selected date).
- All date math uses UTC to avoid daylight-saving shifts.
FAQ
Which week numbering rule should I pick?
ISO is safest for global collaboration: Monday start and Week 1 contains Jan 4. Use simple weeks if your team numbers the week containing Jan 1 as Week 1 and sometimes starts on Sunday.
How are fiscal year labels calculated?
Pick the start month (for example, Apr = 4). “Start year” labeling keeps the first year (FY2025); “End year” uses the closing year (FY2026). The tool also shows the exact start and end dates.
Does this handle week 53 and leap years?
Yes. ISO week-year can include Week 53 for some years, and leap years are handled automatically because calculations use UTC date arithmetic.
How does this compare to Excel (WEEKNUM / ISOWEEKNUM)?
Simple week matches Excel’s WEEKNUM(date,1) (Sunday start) or WEEKNUM(date,2) (Monday start). ISO week matches ISOWEEKNUM(date) (or WEEKNUM(date,21)).
Does this support 4-4-5 or retail calendars?
No. This tool uses month-based calendar quarters and fiscal quarters. If your company uses a 4-4-5 or retail calendar, use the correct reporting system instead of this page.
Comments
Load comments only when you need them.