mnth = DateDiff(DateInterval.Month, 8/30/2012, 10/1/2012) gives mnth = 2. But when we look, there is only 32 days between these dates. I am expecting a result mnth=1 as there is only 32 days between these days.
Pls help..
In my scenario i can consider a 15+ days to be a month but if it is less than 15, it should'nt be considered.
To get the number of complete months you can do different things depending on your interpretation,
Public Function CompleteMonthsBetweenA( _ ByVal start As DateTime, _ ByVal end As DateTime) As Integer Dim invertor = 1 If (start > end) Then Dim tmp = end end = start start = tmp invertor = -1 End If Dim diff = ((end.Year - start.Year) * 12) + end.Month - start.Month If start.Day > end.Day Then Return (diff - 1) * invertor Else Return diff * invertor End If End Function With this function the number of complete months between 31/05/2011 (dd/mm/yy) and 30/06/2011 is 0 but between 30/06/2011 and 31/07/2011 is 1. Which may or may not be what you expect.
Public Function CompleteMonthsBetweenB( _ ByVal start As DateTime, _ ByVal end As DateTime) As Integer Dim invertor = 1 If (start > end) Then Dim tmp = end end = start start = tmp invertor = -1 End If Dim diff = ((end.Year - start.Year) * 12) + end.Month - start.Month Dim startDaysInMonth = DateTime.DaysInMonth(start.Year, start.Month) Dim endDaysInMonth = DateTime.DaysInMonth(end.Year, end.Month) If (start.Day / startDaysInMonth) > (end.Day / endDaysInMonth) Then Return (diff - 1) * invertor Else Return diff * invertor End If End Function With this function the ratio Day / DaysInMonth is taken so the relative completion of the two months can be assessed.
Public Function CompleteMonthsBetweenC( _ ByVal start As DateTime, _ ByVal enddate As DateTime) As Integer Dim invertor = 1 If (start > enddate) Then Dim tmp = enddate enddate = start start = tmp invertor = -1 End If Dim diff = ((enddate.Year - start.Year) * 12) + enddate.Month - start.Month Dim remainingDays = _ (DateTime.DaysInMonth(start.Year, start.Month) - start.Day) + enddate.Day If remainingDays < 15 Then Return (diff - 1) * invertor Else Return diff * invertor End If End Function This function only rounds down if the surplus days are less than the magic number 15, which I think is what you are asking for in your update.
Public Function CompleteMonthsBetweenD( _ ByVal start As DateTime, _ ByVal end As DateTime) As Integer Return end.Subtract(start).TotalDays \ 30.436875 End Function This function takes the simpler approach of dividing the total number of days by the average number of days per month in the Gregorian Calendar.
DateTime is a value type, it cannot be null.The difference in months is calculated without regard to the day component of the dates.
For example, the difference in months between 8/31/2012 and 9/1/2012 is 1, eventhough it's only one day between the dates.
If you want to consider the day component you have to get the date difference in days instead of months, and calculate how many months you want that to be.
This is the class I use (it's C# but really easy to convert to VB.NET). It is usefull for years, months, days... it is ideal for displaying ages in #Y-#M-#D format.
public class DateDifference { /// <summary> /// defining Number of days in month; index 0=> january and 11=> December /// february contain either 28 or 29 days, that's why here value is -1 /// which wil be calculate later. /// </summary> private int[] monthDay = new int[12] { 31, -1, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }; /// <summary> /// contain from date /// </summary> private DateTime fromDate; /// <summary> /// contain To Date /// </summary> private DateTime toDate; /// <summary> /// this three variable for output representation.. /// </summary> private int year; private int month; private int day; public DateDifference(DateTime d1, DateTime d2) { int increment; if (d1 > d2) { this.fromDate = d2; this.toDate = d1; } else { this.fromDate = d1; this.toDate = d2; } /// /// Day Calculation /// increment = 0; if (this.fromDate.Day > this.toDate.Day) { increment = this.monthDay[this.fromDate.Month - 1]; } /// if it is february month /// if it's to day is less then from day if (increment == -1) { if (DateTime.IsLeapYear(this.fromDate.Year)) { // leap year february contain 29 days increment = 29; } else { increment = 28; } } if (increment != 0) { day = (this.toDate.Day + increment) - this.fromDate.Day; increment = 1; } else { day = this.toDate.Day - this.fromDate.Day; } /// ///month calculation /// if ((this.fromDate.Month + increment) > this.toDate.Month) { this.month = (this.toDate.Month + 12) - (this.fromDate.Month + increment); increment = 1; } else { this.month = (this.toDate.Month) - (this.fromDate.Month + increment); increment = 0; } /// /// year calculation /// this.year = this.toDate.Year - (this.fromDate.Year + increment); } public override string ToString() { //return base.ToString(); return this.year + " Year(s), " + this.month + " month(s), " + this.day + " day(s)"; } public int Years { get { return this.year; } } public int Months { get { return this.month; } } public int Days { get { return this.day; } } } USAGE:
DateDifference diff = new DateDifference(date1, date2); int months = (diff.Years*12) + diff.Months + diff.Days > 15 ? 1 : 0; DateTime.DaysInMonth
strAge isn't a number of whole months. You could argue it is a more sensible answer than a bare number but TimeSpan is better still.If you want the number of complete month, then you'll need to compare date that starts at the begining of the closet month.
Sub Main() ' mnth = DateDiff(DateInterval.Month, 8/30/2012, 10/1/2012) Console.WriteLine(GetCompleteMonthCount(New DateTime(2012, 8, 30), New DateTime(2012, 10, 1))) Console.ReadLine() End Sub Public Function GetCompleteMonthCount(ByVal d1 As DateTime, ByVal d2 As DateTime) As Integer If d1.Day <> 1 Then d1 = d1.AddMonths(1) d1 = New DateTime(d1.Year, d1.Month, 1) End If If d2.Day <> 1 Then d2 = New DateTime(d2.Year, d2.Month, 1) End If Return DateDiff(DateInterval.Month, d1, d2) End Function The solutions above are all very good but perhaps a little over-complicated, how about
Function wholeMonthsEd(d1, d2) As Integer ' determine the DateDiff function output ' which gives calendar month difference initMonths = DateDiff("m", d1, d2) ' do calcs on the Day of the month to deduct/not a calendar month If Day(d2) < Day(d1) Then initMonths = initMonths - 1 End If wholeMonths = initMonths End Function 