By Ruben Geert van den Berg on May 29, 2013 under SPSS Glossary.

# Date Variable

## Definition

In SPSS, a date variable is a variable holding the number of seconds since (roughly) the year 1582. It is this format which makes it possible to do date calculations such as adding days to a date.

## SPSS Date Variables

- In SPSS, a date variable is just a number like any other number such as annual income or number of children in a household.
- However, date variables usually hold very large numbers since their actual values are the
**numbers of seconds**since the Gregorian calender started (October 14th, 1582). - The reason for this format is that it renders
**time calculations**as simple as adding and subtracting (large) numbers. - However, these large numbers are
**not easy to read**by most people. Therefore, the dates represented by them can be shown instead of the actual values in numbers of seconds. - This is done by the
`FORMATS`

command. Note that this does not change the underlying number of seconds. It's only**displayed**differently.

## SPSS Date Formats

There are various ways to display dates in SPSS. A date format can be set by (e.g.) `FORMATS birthday (EDATE10).`

Again, note that this does not change the underlying value in seconds. The most common date formats are

**31-DEC-99**(dd-mmm-yy) is referred to as**DATE9**; months are shown as three letter abbreviations and the`9`

refers to the number of characters used by this notation.**31-DEC-1999**(dd-mmm-yyyy) is referred to as**DATE11**.**31.12.99**(dd.mm.yy) is referred to as**EDATE8**(**E**uropean date).**31.12.1999**(dd.mm.yyyy) is referred to as**EDATE10**.**12/31/99**(mm/dd/yy) is referred to as**ADATE8**(**A**merican date).**12/31/1999**(mm/dd/yyyy) is referred to as**ADATE10**.**99/12/31**(yy/mm/dd) is referred to as**SDATE8**(**S**ortable date). It is sortable because its alphabetical order corresponds to its chronological order. This does not hold for the aforementioned formats.**1999/12/31**(yyyy/mm/dd) is referred to as**SDATE10**.

## SPSS Date Functions

- For the number of days (or other time units) between two dates, use the
function. For an example, see Compute Age.`DATEDIFF`

- For extracting a year (or other time unit) from a date, use the
function. For an example, see Extract a Year from a Date.`XDATE`

- For finding what date it will be in 90 days (or other time unit), use the
function. For an example, see Convert Unix Dates into SPSS Dates.`DATESUM`

- For creating an SPSS date value (number of seconds) given a day, month and year, use the
function. For an example, see Convert Numeric to Date Variable.`DATE.DMY`

## SPSS Date Format Demonstration

- This tutorial was written in 2012. So since 1582,
**430 years**have gone by. - A year roughly holds 365.25 days, so that gives us some
**16,000 days**. This comes down to some**3.8 million hours**. - Multiplying by 3600 (the number of seconds per hour) implies that some
**13.6 billion seconds**have passed between 1582 and 2012. - This value may be written as
in SPSS. So entering this value should result in a date close to 2012 after displaying it as a date. Running the syntax below confirms that this is the case.`1.36E10`

## SPSS Date Syntax Example

data list free/now.

begin data

1.36E10

end data

formats now(edate10).

begin data

1.36E10

end data

formats now(edate10).