# Fiscal calendars, ISO-8601 weeks and date math

*Tableau Consultant Study Guide · Design and Troubleshoot Calculations and Workbooks · Last updated November 3, 2026 · https://www.certifyforce.com/study-guide/tableau-consultant/design-and-troubleshoot-calculations-and-workbooks/fiscal-calendars-iso-8601-weeks-and-date-math*

Set a fiscal year start for a data source or a single date field and predict which date parts change, switch to the ISO-8601 week-based calendar for retail and financial weeks, build 4-4-5 style segments, and write DATEADD, DATEPART and DATETRUNC calculations that respect fiscal and ISO rules.

- Certification: Salesforce Tableau Consultant
- Exam section: Design and Troubleshoot Calculations and Workbooks
- Study guide: https://www.certifyforce.com/study-guide/tableau-consultant

**Official exam objective:**

> Implement advanced date functions, such as fiscal calendars.

## What the exam expects

- Choose where to set a fiscal year start (the whole data source or one date field) so existing views show fiscal values without being rebuilt.
- Predict which date parts and truncations change under a fiscal calendar, and how fiscal years and quarters are labelled.
- Decide when a reporting calendar needs the ISO-8601 week-based calendar rather than a Gregorian calendar with a different week start.
- Split ISO quarters into 4-4-5 or other week patterns with a calculation.
- Write row-level fiscal and ISO date math with DATEADD, DATEPART and DATETRUNC, including the `start_of_week` argument.

Key terms:
- **Fiscal year start:** the month a data source or date field treats as the first month of the year.
- **ISO-8601 week-based calendar:** a calendar of ISO years, quarters, weeks and weekdays with Monday-start weeks that never span two years.
- **Date truncation:** rounding a date down to the start of a level, as DATETRUNC does.
- **start_of_week:** the optional function argument that overrides the data source's Week start.

## Key facts

| Fact | Detail | Source |
|---|---|---|
| Data source fiscal start | Date Properties > Fiscal year start, applied to the data source overall | [Date Properties for a Data Source](https://help.tableau.com/current/pro/desktop/en-us/date_properties.htm) |
| Field fiscal start | Default Properties > Fiscal Year Start; applies to all instances of the field in the workbook | [Fiscal Dates](https://help.tableau.com/current/pro/desktop/en-us/dates_fiscal.htm) |
| Fiscal data source type | Relational data sources only | [Fiscal Dates](https://help.tableau.com/current/pro/desktop/en-us/dates_fiscal.htm) |
| FY prefix | Year and Quarter levels only | [Fiscal Dates](https://help.tableau.com/current/pro/desktop/en-us/dates_fiscal.htm) |
| MM/YYYY and M/D/Y | Always show calendar dates | [Fiscal Dates](https://help.tableau.com/current/pro/desktop/en-us/dates_fiscal.htm) |
| ISO year length | 52 or 53 weeks | [ISO-8601 Week-Based Calendar](https://help.tableau.com/current/pro/desktop/en-us/dates_calendar.htm) |
| ISO quarters | First three have 13 weeks; the last has 13 or 14 | [ISO-8601 Week-Based Calendar](https://help.tableau.com/current/pro/desktop/en-us/dates_calendar.htm) |
| ISO weekday numbers | Monday 1 through Sunday 7 | [ISO-8601 Week-Based Calendar](https://help.tableau.com/current/pro/desktop/en-us/dates_calendar.htm) |
| `iso-week` start | Always Monday | [Date Functions](https://help.tableau.com/current/pro/desktop/en-us/functions_functions_date.htm) |
| start_of_week omitted | The data source decides | [Date Functions](https://help.tableau.com/current/pro/desktop/en-us/functions_functions_date.htm) |

## Check yourself

- Why can't a consultant set Week start on a multidimensional (cube) data source?
- When a custom date format uses only the "y" and "q" placeholders on a fiscal date field, what appears?
- Why does truncating an ISO-8601 date at 'month' still return a week start?
- Which number does ISOWEEKDAY return for a Sunday?

## Sources

- [Fiscal Dates](https://help.tableau.com/current/pro/desktop/en-us/dates_fiscal.htm)
- [ISO-8601 Week-Based Calendar](https://help.tableau.com/current/pro/desktop/en-us/dates_calendar.htm)
- [Date Functions](https://help.tableau.com/current/pro/desktop/en-us/functions_functions_date.htm)
- [Date Properties for a Data Source](https://help.tableau.com/current/pro/desktop/en-us/date_properties.htm)

## About the full unit

The "Core concepts", "Exam traps" and "Worked scenario" sections of this unit, its 7 linked practice questions, and unlimited timed mock exams are included with the Tableau Consultant pack (USD $19): https://www.certifyforce.com/practice-exams