Chapter Contents



Date and Time Intervals


is an integer representing the difference, in number of days, between any two dates or times or datetimes.

is a unit of measurement that SAS can count within an elapsed period of time, such as DAYS, TENDAYS and SEMIMONTHS.


SAS provides date, time, and datetime intervals for counting different periods of elapsed time. You can create multiples of the intervals and shift their starting point. Use them with the INTCK and INTNX functions and with procedures that support numbered lists (such as the PLOT procedure). The form of an interval is


The terms in an interval have the following definitions:

is the name of the interval. See the following table for a list of intervals and their definitions.

creates a multiple of the interval. Multiple can be any positive number. The default is 1. For example, YEAR2 indicates a two-year interval.

is the starting point of the interval. By default, the starting point is 1. A value greater than 1 shifts the start to a later point within the interval. The unit for shifting depends on the interval, as shown in the following table. For example, YEAR.3 specifies a yearly period from the first of March through the end of February of the following year.

Intervals By Category

Intervals Used with Date and Time Functions
Category Interval Definition Default Starting Point Shift Period Example Description
Date DAY Daily intervals Each day Days DAY3 Three-day intervals starting on Sunday

WEEK Weekly intervals Each Sunday Days (1=Sunday ... 7=Saturday WEEK.7 Weekly with Saturday as the first day of the week



Daily intervals with weekend days treated as part of the preceding weekday. Days identifies the weekend days by number (1=Sunday ... 7=Saturday). By default, days=17. Each day Days WEEKDAY1W


Six-day week with Sunday as a weekend day

Five-day week with Tuesday and Thursday as weekend days (W indicates that day 3 and day 5 are weekend days)

TENDAY Ten-day intervals (a U.S. automobile industry convention) First, eleventh, and twenty-first of each month TENDAY periods TENDAY4.2 Four ten-day periods starting at the second TENDAY period

SEMIMONTH Half-month intervals First and sixteenth of each month SEMIMONTH periods SEMIMONTH2.2 Intervals from the sixteenth of one month through the fifteenth of the next month

MONTH Monthly intervals First of each month Months MONTH2.2 February-March, April-May, June-July, August-September, October-November, and December-January of the following year

QTR Quarterly (three-month) intervals January 1 April 1 July 1 October 1 Months QTR3.2 three-month intervals starting on April 1, July 1, October 1, and January 1
April 1
July 1
October 1

SEMIYEAR Semiannual (six-month) intervals January 1 Months SEMIYEAR.3 Six-month intervals, March-August and September-February
July 1

YEAR Yearly intervals January 1 Months

Datetime Add DT To any date interval

Time SECOND Second intervals Each second Seconds

MINUTE Minute intervals Each minute Minutes

HOUR Hourly intervals Each hour Hours

Example 3: Calculating a Duration

This program reads the project start and end dates and calculates the duration between them.

data projects;
options nodate pageno=1 linesize=80 pagesize=60;    
   input Projid startdate date9. enddate date9.;
398 17oct1997 02nov1997
942 22jan1998 10mar1998
167 15dec1999 15feb2000
250 04jan2001 11jan2001

proc print data=projects;
   format startdate enddate date9.;
      title 'Days Between Project Start and Project End';

Output from the PRINT Procedure
             Days Between Project Start and Project End run                8

            Obs    Projid    Startdate      Enddate    Duration

             1       398       17OCT1997  02NOV1997       16   
             2       942       22JAN1998  10MAR1998       47   
             3       167       15DEC1999  15FEB2000       62   
             4       250       04JAN2001  11JAN2001        7   

Boundaries of Intervals

The SAS System associates date and time intervals with fixed points on the calendar. For example, the MONTH interval represents the time from the beginning of one calendar month to the next, not a period of 30 or 31 days. When you use date and time intervals (for example, with the INTCK or INTNX functions), the SAS System bases its calculations on the calendar divisions that are present. Consider the following examples:

Example Results Explanation
mnthnum1=1 The number of MONTH intervals the INTCK function counts depends on whether the first day of a month falls within the period.
next represents 01sep2000 The INTNX function produces the SAS date value that corresponds to the beginning of the next interval.

Note:   The only intervals that do not begin on the same date in each year are WEEK and WEEKDAY. A Sunday can occur on any date because the year is not divided evenly into weeks.  [cautionend]

Single-Unit Intervals

Single-unit intervals begin at the following points on the calendar:

Single-Unit Intervals
These single-unit intervals Begin at this point on the calendar
DAY and WEEKDAY each day
each Sunday
the first, eleventh, and twenty-first of each month
SEMIMONTH the first and sixteenth of each month
the first of each month
the first of January, April, July and October
the first of January and July
the first of January

Single-unit time intervals begin as follows:

Single-Unit Time Intervals
These single-unit time intervals Begin at this point
SECOND each second
MINUTE each minute
HOUR each hour

Multiunit Intervals

Multiunit Intervals Other Than Multiweek Intervals

Multiunit intervals, such as MONTH2 or DAY50, also depend on calendar measures, but they introduce a new problem: the SAS System can find the beginning of a unit (for example, the first of a month), but where does that unit fall in the interval? For example, does the first of October mark the first or the second month in a two-month interval?

For all multiunit intervals except multiweek intervals, the SAS System creates an interval beginning on January 1, 1960, and counts forward from that date to determine where individual intervals begin on the calendar. As a practical matter, when a year can be divided evenly by an interval, think of the intervals as beginning with the current year. Thus, MONTH2 intervals begin with January, March, May, July, September, and November. Consider this example:

Month2 Intervals
SAS statements Results





In the above example, the SAS System counts 50 days beginning with January 1, 1960; then another 50 days; and so on. As part of this count, the SAS System counts one DAY50 interval between October 1, 1998 and January 1, 1999. As an example, to determine the date on which the next DAY50 interval begins, use the INTNX function, as follows:

Using the INTNX Function
SAS statements Results


SAS date value 14200, or Nov 17, 1998

The next interval begins on November 17, 1998.

Time intervals (those that represent divisions of a day) are aligned with the start of the day, that is, midnight. For example, HOUR8 intervals divide the day into the periods 00:00 to 08:00, 8:00 to 16:00, and 16:00 to 24:00 (the next midnight).

Multiweek Intervals

Multiweek intervals, such as WEEK2, present a special case. In general, weekly intervals begin on Sunday, and the SAS System counts a week whenever it passes a Sunday. However, the SAS System cannot calculate multiweek intervals based on January 1, 1960, because that date fell on a Friday, as shown:

Calculating Multi Week Intervals


Therefore, the SAS System begins the first interval on Sunday of the week containing January 1, 1960--that is, on Sunday, December 27, 1959. The SAS System counts multiweek intervals from that point. The following example counts the number of two-week intervals in the month of August, 1998:

Counting Two-Week Intervals
SAS statements Results

('week2','01aug98'D, '31aug98'D); 


To see the beginning date of the next interval, use the INTNX function, as shown here:

Using INTNX to See The Beginning Date of an Interval
SAS statements Results


"Begin" represents SAS date 14093 or August 02, 1998

The next interval begins on August 16.

Shifted Intervals

Shifting the beginning point of an interval is useful when you want to make the interval represent a period in your data. For example, if your company's fiscal year begins on July 1, you can create a year beginning in July by specifying the YEAR.7 interval. Similarly, you can create a period matching U.S. presidential elections by specifying the YEAR4.11 interval. This section discusses how to use shifted intervals and how the SAS System creates them.

How to Use Shifted Intervals

When you shift a time interval by a subperiod, the shift value must be less than or equal to the number of subperiods in the interval. For example, YEAR.12 is valid (yearly periods beginning in December), but YEAR.13 is not. Similarly, YEAR2.25 is not valid because there is no twenty-fifth month in the two-year period.

In addition, you cannot shift an interval by itself. For example, you cannot shift the interval MONTH because the shifting subperiod for MONTH is one month and MONTH contains only one monthly subperiod. However, you can shift multi-unit intervals by the subperiod. For example, MONTH2.2 specifies bimonthly periods starting on the first day of the second month.

How the SAS System Creates Shifted Intervals

For all intervals except those based on weeks, the SAS System creates shifted intervals by creating the interval based on January 1, 1960, by moving forward the required number of subperiods, and by counting shifted intervals from that point. For example, suppose you create a shifted interval called DAY50.5. The SAS System creates a 50-day interval in which January 1, 1960 is day 1. The SAS System then moves forward to day 5. (Note that the difference, or amount of movement, is 4 days.) The SAS System begins counting shifted intervals from that point. The INTNX function demonstrates that the next interval begins on January 5, 1960:

Using INTNX to Determine When an Interval Begins
SAS statements Results


SAS date value 4, or Jan 5, 1960

For shifted intervals based on weeks, the SAS System first creates an interval based on Sunday of the week containing January 1, 1960 (that is, December 27, 1959), then moves forward the required number of days. For example, suppose you want to create the interval WEEK2.8 (biweekly periods beginning on the second Sunday of the period). The SAS System measures a two-week interval based on Sunday of the week containing January 1, 1960, and begins counting shifted intervals on the eighth day of that. The INTNX function shows the beginning of the next interval:

Using the INTNX Function to Show the Beginning of the Next Interval
SAS statements Results


SAS date value 2, or Jan 3, 1960

You can also shift time intervals. For example, HOUR8.7 intervals divide the day into the periods 06:00 to 14:00, 14:00 to 22:00, and 22:00 to 06:00.

Chapter Contents



Top of Page

Copyright 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.