Incrementing and Decrementing Dates

Restriction: This topic applies to Windows environments only.

When adding durations to dates or subtracting durations from dates, the results are dates between January 1, 0001 and December 31, 9999.

Adding/Subtracting Years
When a duration of years is added or subtracted, only the year portion of the date is affected (except for February 29). If the result of the calculation would be February 29 of a non-leap year, the day portion of the result is set to February twenty-eighth.
Adding/Subtracting Months
When a duration of months is added or subtracted, the month is changed and if necessary, the year. The day portion of the date is changed only if the result would be an invalid date (such as September 31). In this case, the day is set to the last day of the month.
Adding/Subtracting Days
When a duration of days is added or subtracted, the day will change and if necessary the month and year.

Both positive and negative durations can be added or subtracted when working with date arithmetic. The sequence in which the date is incremented (or decremented) depends on the following:
- When a positive date duration is added to a date or when a negative date duration is subtracted from a date, the date is incremented by the specified years, months and days in that order.
  For example, entering DATE1+x, where x is a positive decimal number, is equivalent to the expression:
```
DATE1 + YEAR(x) YEARS + MONTH(x) MONTHS + DAY(x) DAYS
```
- When a positive date duration is subtracted from a date or a negative date duration is added to a date, the date is decremented by the specified number of days, months and years in that order.
  For example, entering DATE1-x, where x is a positive decimal number, is equivalent to the expression:
```
DATE1 - DAY(x) DAYS - MONTH(x) MONTHS - YEAR(x) YEARS
```