Partial opening week, year seam, full weeks, and partial closing weekUpdates with every input
Date & Time
Week Number Duration Calculator
Measure an inclusive ISO-week span across a year boundary, translate it into calendar and scheduled workdays, and preserve partial first and last weeks instead of assuming every selected week contributes seven full days.
Inclusive ISO week labels touched—
Inclusive calendar-day duration—
Equivalent full weeks—
Additional days beyond full weeks—
Scheduled workdays in span—
Net workdays after holidays—
Productive-hour capacity—
Cross-year span interpretation—
ISO week-year bridge
Partial opening week, year seam, full weeks, and partial closing week
A continuous week ruler crosses the ISO-year seam. Filled day cells show the inclusive span, while scheduled workdays and holidays remain a second capacity layer.
Week-by-week duration ledger
Included days and work capacity for every ISO week touched
Review partial boundary weeks, year labels, scheduled days, allocated holidays, net days, and productive hours.
| ISO week | Year side | Included weekdays | Calendar days | Scheduled days | Holidays | Net workdays | Productive hours |
|---|
ISO span setup
Define both week labels and boundary weekdays
- Confirm whether the start ISO year has 52 or 53 weeks.
- Choose the start week and weekday.
- Choose the end week in the following ISO year.
- Set the weekly work pattern.
- Deduct only holidays that displace scheduled work.
Week-number logic
Week labels are coordinates, not durations
The same pair of week numbers can represent different durations when boundary weekdays change.
ISO year seams may contain week 53, so the start-year week count must be explicit before placing next-year week numbers on a continuous axis.
Calculation method
Convert ISO week labels to one continuous day index
The start position is measured inside the start year. The end week is placed after all weeks in the start year, allowing the duration to cross a 52- or 53-week seam without ambiguous subtraction.
Detailed calculation process and general formulas
s = 7(Wₛ − 1) + (dₛ − 1)e = 7Y + 7(Wₑ − 1) + (dₑ − 1)D = e − s + 1F = ⌊D/7⌋; R = D mod 7N = max(S − H, 0); capacity = NhSymbols, meanings, and units
- Y
- number of ISO weeks in the start yearweeks
- Wₛ
- start ISO week numberweek index
- Wₑ
- end ISO week number in the next yearweek index
- D
- inclusive calendar durationdays
- H
- holidays displacing scheduled workdaysdays
Span interpretation
Read duration, label coverage, and work capacity separately
The calculator reports four related but noninterchangeable measures.
Labels touched
—ISO week rows with at least one included day.
Inclusive duration
—Calendar days including both endpoints.
Net work supply
—Scheduled days after holidays.
Productive capacity
—Net workdays converted with productive hours.
Decision takeaway: Use the continuous-day duration for elapsed time and the net-workday layer for capacity.
ISO calendar checks
Avoid week-year boundary errors
- Verify the ISO week year, not only calendar year.
- Check whether week 53 exists.
- State whether endpoints are inclusive.
- Do not subtract week numbers across a year seam directly.
Week-span evidence
Calendar facts needed for a reliable duration
- ISO-8601 week calendar
- Start and end weekday records
- Organization work pattern
- Holiday calendar
- Productive-hours assumption
Practical applications
Decisions this calculator is designed to support
Cross-year delivery window
A project runs from Wednesday of ISO week 48 through Friday of next year's week 6.
What the result clarifies: The bridge includes partial boundary weeks and the full year seam without an off-by-one error.
Seasonal staffing capacity
A staffing plan spans year end, excludes four workday holidays, and uses 7.5 productive hours per day.
What the result clarifies: The work-capacity layer is lower than the raw calendar duration.
Worked example
Current-input substitution and reconciliation
Model limitations
The end week is intentionally interpreted in the following ISO year. The calculator does not derive real calendar dates or validate whether a manually entered week 53 exists for a specific named year.
Week Number Duration Calculator FAQ
Why enter the number of weeks in the start year?
It locates the next year's week numbers after a 52- or 53-week seam.
Are start and end days included?
Yes. Calendar duration is inclusive of both endpoints.
What are week labels touched?
The number of ISO week rows containing at least one included day.
Can the end week be in the same year?
This calculator is designed specifically for a next-ISO-year endpoint.