5.3 Working with SAS Dates, Times, & Intervals

5.3 Working with SAS Dates, Times, & Intervals

Handling calendar dates, clock times, and time-series intervals is a cornerstone of business analytics. SAS handles date and time values using a unique internal numeric representation. Understanding how SAS stores date values, how formats display them, and how date functions calculate intervals is vital for writing bug-free programs and passing the SAS Base exam.

---

1. Internal Storage of SAS Dates, Times, & Datetimes

Rather than storing dates as text strings (such as "2026-01-01"), SAS stores all date and time values as internal numeric values relative to specific baseline epochs:

• SAS Date Value: An integer representing the number of days between January 1, 1960 and the specified date.
  • January 1, 1960 = 0
  • January 2, 1960 = 1
  • December 31, 1959 = -1
  • January 1, 2026 = 24107
• SAS Time Value: A numeric value representing the number of seconds past midnight (ranges from 0 to 86400).
• SAS Datetime Value: A numeric value representing the number of seconds between midnight on January 1, 1960 and the specified date/time.

Date, Time, and Datetime Literals

To write literal date, time, or datetime constants directly in SAS code, enclose the string in single or double quotes followed immediately by d, t, or dt:

data work.literals;
    d_val  = '01JAN2026'd;     /* SAS date value: 24107 */
    t_val  = '14:30:00't;      /* SAS time value: 52200 seconds */
    dt_val = '01JAN2026:14:30:00'dt; /* SAS datetime value */
run;

---

2. Date Creation & Extraction Functions

SAS provides built-in functions to build date values from individual components and to extract components from existing SAS date values.

Building Dates: MDY and DATEJUL

• MDY(month, day, year): Creates a SAS date value from month (1–12), day (1–31), and year values.
• DATEJUL(julian_date): Converts a 5-digit or 7-digit Julian date (YYDDD or YYYYDDD) into a SAS date value.
• TODAY() or DATE(): Returns the current date as a SAS date value based on the system clock. The two are aliases and return an identical value.
• TIME(): Returns the current clock time as a SAS time value — seconds past midnight, not a date. Apply a TIME8. format to display it as hh:mm:ss.

TODAY(), DATE(), and TIME() take no arguments, but the empty parentheses are still required: writing current = today; creates an uninitialized variable named today rather than calling the function, which is a classic exam distractor.

data work.build_dates;
    m = 7; d = 4; y = 2026;
    july4th = mdy(m, d, y);            /* Returns SAS date for July 4, 2026 */
    current = today();                 /* Current system date */
    clock   = time();                  /* Current time, seconds past midnight */
    format july4th current date9. clock time8.;
run;

Extracting Date Components

Given a valid SAS date integer, you can extract specific calendar components. The exam names four extraction functions explicitly — YEAR, QTR, MONTH, and DAY:

data work.extract_dates;
    sample_date = '15AUG2026'd;
    
    day_num   = day(sample_date);     /* Returns 15 */
    month_num = month(sample_date);   /* Returns 8  */
    qtr_num   = qtr(sample_date);     /* Returns 3 (August sits in Quarter 3) */
    year_num  = year(sample_date);    /* Returns 2026 */
    wday_num  = weekday(sample_date); /* Returns 7 (1=Sunday, 7=Saturday) */
run;

[!WARNING] Do not confuse the QTR() function with the 'QTR' interval string. qtr(d) takes a date argument and returns the quarter number 1–4. intck('QTR', d1, d2) and intnx('QTR', d, 1) pass 'QTR' as a quoted interval name to a different function entirely. The same trap applies to YEAR, MONTH, and DAY, which are all both extraction functions and interval names.

---

3. Interval Counting with INTCK

The INTCK function counts the number of interval boundaries crossed between two SAS date, time, or datetime values.

$\text{Syntax: } \text{INTCK}('\textit{interval}', \textit{start-date}, \textit{end-date}, <'\textit{method}'>)$

Supported intervals include 'DAY', 'WEEK', 'MONTH', 'QTR', 'YEAR', 'HOUR', 'MINUTE', 'SECOND'.

[!IMPORTANT] INTCK does not count the number of complete elapsed periods; it counts how many discrete interval boundaries (e.g., midnight for days, January 1 for years, first of the month for months) lie between start-date and end-date.

data work.intck_demo;
    d1 = '31DEC2025'd;
    d2 = '01JAN2026'd;
    
    /* Only 1 day has elapsed, but a Year boundary was crossed! */
    years_crossed  = intck('YEAR', d1, d2);   /* Returns 1 */
    months_crossed = intck('MONTH', d1, d2);  /* Returns 1 */
    days_crossed   = intck('DAY', d1, d2);    /* Returns 1 */
run;

To count discrete intervals using continuous boundaries (exact elapsed duration), SAS 9.4 allows passing 'CONTINUOUS' or 'C' as the fourth argument:

/* Continuous method checks full 365-day duration */
actual_years = intck('YEAR', d1, d2, 'C'); /* Returns 0 */

---

4. Date Adjustments with INTNX

The INTNX function advances or increments a SAS date, time, or datetime value by a specified number of intervals and aligns the resulting value within that interval.

$\text{Syntax: } \text{INTNX}('\textit{interval}', \textit{start-date}, \textit{increment}, <'\textit{alignment}'>)$

Alignment Options:

• 'BEGINNING' or 'B': Aligns the date to the first day of the target interval (default).
• 'MIDDLE' or 'M': Aligns the date to the midpoint of the target interval.
• 'END' or 'E': Aligns the date to the last day of the target interval.
• 'SAME' or 'S': Preserves the same relative day position within the target interval.

data work.intnx_demo;
    start = '15MAY2026'd;
    
    next_month_beg  = intnx('MONTH', start, 1, 'B'); /* 01JUN2026 */
    next_month_end  = intnx('MONTH', start, 1, 'E'); /* 30JUN2026 */
    next_month_same = intnx('MONTH', start, 1, 'S'); /* 15JUN2026 */
    prev_qtr_end    = intnx('QTR', start, -1, 'E');  /* 31MAR2026 */
run;

---

5. Precise Age & Year Calculation: YRDIF

The YRDIF function calculates the exact fractional difference in years between two SAS dates according to a specified day-count basis.

$\text{Syntax: } \text{YRDIF}(\textit{start-date}, \textit{end-date}, '\textit{basis}')$

Common basis standards include 'ACT/ACT' (actual days / actual year length), '30/360', and 'ACT/360'.

data work.yrdif_demo;
    dob = '15MAY1990'd;
    ref = '15NOV2026'd;
    age = yrdif(dob, ref, 'ACT/ACT'); /* Returns 36.5041... */
run;