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# 4GuysFromRolla.com : ASP FAQS : Dates and Times

Question:

## How can I determine the number of days in a given month?

[Print this FAQ]

Answer: VBScript offers a number of great date functions that can be used in tandem to calculate all sorts of date-related information! One useful function is `DateSerial`, which constructs a date given a year, month, and day as its three parameters. For example:

 `Dim myDatemyDate = DateSerial(1978, 8, 1)Response.Write "I was born on " & myDate`

will produce the output:
`I was born on 8/1/78`

Another neat function is `Day`, which will return the day (1 to 31) part of a date. Yet another neat function is `DateAdd`, which can be used to add various intervals to a date. It takes the form:

 `retDate = DateAdd(interval, number, date)`

The `interval` can be a day, a week, a quarter, a year, a month, a weekday... all sorts of things! (For a full listing of options be sure to read the `DateAdd` technical docs.)

With these three functions in tandem, we can write a short function that will return the number of days for a given month in a given year. Observe:

 `Function NumberOfDays(iMonth, iYear)  NumberOfDays = Day(DateAdd("d", -1, _                          DateSerial(iYear, iMonth + 1, 1)))End Function`

The `NumberOfDays` function takes two parameters, a month and year, and calculates the number of days in the month/year. It does this by saying, "What is the day number of the day one day before the first day of the next month?" Pretty neat! A bit wordy, I know, but examine the code and see if you can't determine what it's doing. It's using `DateSerial` to get the date for the 1st of the month, one month ahead of the passed in month. (`DateSerial` is smart enough to know to increment `iYear` if `iMonth` is 12 (December)...) Once we have this new date, we use `DateAdd` to add -1 days, which gives us the date of the last day of `iMonth`. Finally, we use the `Day` function to pick out just the day number itself. Incredibly cool.

 ` The EASIER way! `

Just read the docs for DateSerial! They even demonstrate getting the last day of a month in one of the examples. So:

 `Function NumberOfDays(iMonth, iYear) NumberOfDays = Day( DateSerial( iYear, iMonth + 1, 0 ) )End Function`

Even cooler?

Date Functions in VBScript
`DateAdd` technical docs
`DateSerial` technical docs

Happy Programming!

FAQ posted by Scott Mitchell at 10/6/2000 3:23:00 PM to the Dates and Times category. This FAQ has been viewed 51,270 times.

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