# Date functions

Date functions are provided to manipulate FastStats date fields.

## Today

Returns today’s date shifted by n days.

Expression

```apteco
Today(n)
```

For example:

- `Today(0)` is today’s date
- `Today(1)` is tomorrow
- `Today(-1)` is yesterday
- `Today(-7)` is one week ago

## AgeDays

Age of date in days relative to today.

Expression

```apteco
AgeDays([Date])
```

For example, if today is 30<sup>th</sup> May 2007 and date1 is 20<sup>th</sup> May 2007, `AgeDays(date1)` = 10.

## AgeQuarters

Age of date in 3 calendar month periods relative to today

Expression

```apteco
AgeQuarters([Booking Date])
```

For example, if today is 12 October 2011 and `date1` = 05 January 2011, `AgeQuarters (date1)` = 3.

## AgeWeeks

Age of date in whole weeks relative to today

Expression

```apteco
AgeWeeks([Booking Date])
```

For example, if today is 30 May 2007 and `date1` is 20 May 2007, `AgeWeeks(date1)` = 1.

## AgeMonths

Age of date in months relative to today

Expression

```apteco
AgeMonths([Booking Date])
```

For example, if today is 30 May 2007 and `date1` is 20 May 2006, `AgeMonths (date1)` = 12.

## AgeYears

Age of date in years relative to today

Expression

```apteco
AgeYears([Booking Date])
```

For example, if today is 30 May 2007 and `date1` = 20 May 2005, `AgeYears (date1)` = 2.

## DateDay

Day of date 1.. 31

Expression

```apteco
DateDay([Booking Date])
```

## DateWeek

Week of date 1..53

Expression

```apteco
DateWeek([Booking Date])
```

## DateMonth

Month of date 1=Jan, 2=Feb, … 12=Dec

Expression

```apteco
DateMonth([Booking Date])
```

## DateQuarter

Quarter of date 1=Q1, 2=Q2, 3=Q3, 4=Q4

Expression

```apteco
DateQuarter([Booking Date])
```

## DateYear

Year of date e.g. 2005

Expression

```apteco
DateYear([Booking Date])
```

## DayOfWeek

Day of date 1=Monday, 2=Tuesday, … 7=Sunday

Expression

```apteco
DayOfWeek([Booking Date])
```

## Date2Days

The number of days since 0000

Expression

```apteco
Date2Days(2006,01,01)
```

## DateDiff

Calculates `[Date]` - `[Date]` measured in the specified units (years, quarters, months, weeks, days).

Expression

```apteco
DateDiff( [Date], [Date], "Units")
```

Units specifier is optional. If missing, the default units are days. If only one date is specified, the given date is compared to today.

For example:

- `DateDiff([DepartureDate],[Booking Date],”Days”)` is the number of days between departure and booking.
- `DateDiff([DepartureDate],20051231,”Days”)` is the number of days between departure and 31 Dec 2005.
- `DateDiff([DepartureDate],Today(0),”Days”)` is the number of days until departure.
- `DateDiff([DepartureDate],[Booking Date],”Weeks”)` is the number of weeks between departure and booking.

The zero band extends in both a forward and backward direction from the reference date. An optional final parameter can be set to 1 to return missing value if the first date is after the second date. This ensures that results are only returned when there is a positive value, which corresponds to when the date parameters are in chronological order.

For example:

## MakeDate

Makes a constant date from numbers

Expression

```apteco
MakeDate(Years, Months, Days)
```

For example:

Expression

```apteco
MakeDate(2007,08,22)
```

The expression below returns the start of the year in which the booking was made.

Expression

```apteco
MakeDate(DateYear([Booking Date],01,01))
```

## DateShift

Shift a time by a number of units (years, quarters, months, weeks, days).

Expression

```apteco
DateShift([Date],[Date],"Units")
```

For example:

- `DateShift([BookingDate],30,”Days”)` calculates 30 days after booking.
- `DateShift([DepartureDate],-30,”Days”)` calculates 30 days before departure.
- `DateShift([DOB],18,"Years")` calculates 18<sup>th</sup> birthday

## DayOfYear

Calculates the day number in the year 1 .. 366

Expression

```apteco
DayOfYear([date])
```

For example, the expression below equals 5.

Expression

```apteco
DayOfYear(20070105)
```

## BuildDate

The FastStats system build date shifted by n days.

Expression

```apteco
BuildDate(n)
```

For example:

- `BuildDate(0)` = build date
- `BuildDate(-1)` = day before build date

## Legacy date functions

These are provided for backwards compatibility, but have been superceded by more useful date functions.

### Day

Number of days from year 0000 to date.

Expression

```apteco
Day([Booking Date])
```

### Week

Number of weeks from year 0000 to date.

Expression

```apteco
Week([Booking Date])
```

### Month

Number of months from year 0000 to date.

Expression

```apteco
Month([Booking Date])
```

### Year

Number of years from year 0000 to date.

Expression

```apteco
Year([Booking Date])
```