> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cfo.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Date-part functions

Date-part functions return a numeric part of a date.

## year

Returns the four-digit year.

```text theme={null}
year(Date.Month)
```

## month

Returns the month as a number from 1 to 12.

```text theme={null}
month(Date.Month)
```

## day

Returns the day of the month from 1 to 31.

```text theme={null}
day(Date.Day)
```

## quarter

Returns the calendar quarter from 1 to 4.

```text theme={null}
quarter(Date.Month)
```

## half

Returns 1 for January through June and 2 for July through December.

```text theme={null}
half(Date.Month)
```

## weekday

Returns the day of the week as a number.

```text theme={null}
weekday(Date.Day)
weekday(Date.Day, 2)
```

Without a return type, Sunday is 1 and Saturday is 7. Optional Excel-compatible return types control the starting day and numbering.

## weeknum

Returns the week number within the year.

```text theme={null}
weeknum(Date.Week)
weeknum(Date.Week, 21)
```

The optional return type follows Excel. Return type 21 uses ISO weeks.

## isoweeknum

Returns the ISO 8601 week number.

```text theme={null}
isoweeknum(Date.Week)
```

This is equivalent to `weeknum(Date.Week, 21)`.