how to calculate birthdate from age (day , month ,year) and current date in vb.net

Question

How to calculate birthdate based on age (day, month,year) and current date I tried this but the result appears incorrect I can get age from birth date correctly but getting birth date from age, result appear different than origin birth date sample when calculate age for 15/4/2022 and then calculate birth date for this age it appears 12/4/2022

Dim day, month, year As Integer
    day = CInt(NumDay.Value)
    month = CInt(NumMonth.Value)
    year = CInt(NumYear.Value)
    Dim dateResult As Date = Now
    DateTimePicker1.Value = dateResult.AddYears(-year).AddMonths(-month).AddDays(-day)

enter code here

  Function AgeCalculator(ByVal FromDate As Date, Todate As Date, ByRef year As Integer, ByRef month As Integer, ByRef day As Integer, Optional flgyearOnly As Boolean = False) As String '23/11/2017
    If Not IsDate(FromDate) Then Return ""
    Dim tmpYear As String = "", tmpMonth As String = ""
    Dim tmpdiffDaya As Integer = 0
    Dim tmpAge As String = ""
    tmpdiffDaya = CInt(DateDiff(DateInterval.Day, (FromDate), Todate))
    If tmpdiffDaya <= 0 Then Return ""
    If tmpdiffDaya > 0 And tmpdiffDaya <= 29 Then
        Return tmpdiffDaya & " Days"
    End If
    If tmpdiffDaya = 30 Then
        Return " 1 Month"
    End If
    tmpYear = CStr(tmpdiffDaya / 365)
    If InStr(tmpYear, ".") > 0 Then
        tmpYear = Microsoft.VisualBasic.Left(tmpYear, InStr(tmpYear, ".") - 1)
    End If
    year = CInt(tmpYear)
    If Val(tmpYear) = 0 Then tmpYear = ""
    If Val(tmpYear) > 0 Then
        tmpAge = tmpYear & " years"
        If flgyearOnly Then Return tmpAge
    End If

    tmpdiffDaya = CInt((tmpdiffDaya - (Val(tmpYear) * 365)))

    tmpMonth = CStr(tmpdiffDaya / 30)
    If InStr(tmpMonth, ".") > 0 Then
        tmpMonth = Microsoft.VisualBasic.Left(tmpMonth, InStr(tmpMonth, ".") - 1)

    End If
    month = CInt(tmpMonth)

    If Val(tmpMonth) = 0 Then
        tmpMonth = ""
    Else

        If CInt(tmpMonth) > 0 Then
            tmpAge &= "  " & tmpMonth & " Months"
        End If

    End If
    tmpdiffDaya = CInt((tmpdiffDaya - (Val(tmpMonth) * 30)))
    day = tmpdiffDaya
    If Val(tmpdiffDaya) > 0 Then
        tmpAge &= "  " & tmpdiffDaya & " Days"
    End If
    Return tmpAge
End Function

Answer 1

You need to call AddDays first, then AddMonths , then AddYears . If you wanted to calculate a person's age in years, months and days then you would calculate the years first, then the months, then the days. If you're doing the calculation the other way, you have to actually do it the other way. If you subtract years first then a leap year could throw the calculation out. If you subtract months before days then that calculation will be affected by the different numbers of days in each month.

Private Function GetPastDate(years As Integer, months As Integer, days As Integer) As Date
    Return Date.Today.AddDays(-days).AddMonths(-months).AddYears(-years)
End Function

My date of birth is June 19, 1969, which means that I am 53 years, 1 month and 16 days old today (August 4, 2022). If I use the method above with those numbers then I get the correct date of birth. If I call those methods the opposite way around, I get June 18 instead of 19.

EDIT:

I haven't looked closely but it appears that your AgeCalculator doesn't work. I just tested the following code:

Module Module1

    Sub Main()
        Dim dateOfBirth = #4/15/2012#
        Dim years As Integer
        Dim months As Integer
        Dim days As Integer

        CalculateAge(dateOfBirth, years, months, days)

        Dim output = GetPastDate(years, months, days)
    End Sub

    Private Sub CalculateAge(dateOfBirth As Date, ByRef years As Integer, ByRef months As Integer, ByRef days As Integer)
        Dim temp As Date
        Dim currentDate = Date.Today

        dateOfBirth = dateOfBirth.Date

        years = 0
        months = 0

        Do
            temp = dateOfBirth.AddYears(1)

            If temp > currentDate Then
                Exit Do
            End If

            years += 1
            dateOfBirth = temp
        Loop

        Do
            temp = dateOfBirth.AddMonths(1)

            If temp > currentDate Then
                Exit Do
            End If

            months += 1
            dateOfBirth = temp
        Loop

        days = (currentDate - dateOfBirth).Days
    End Sub

    Private Function GetPastDate(years As Integer, months As Integer, days As Integer) As Date
        Return Date.Today.AddDays(-days).AddMonths(-months).AddYears(-years)
    End Function

End Module

and it worked as expected. The values of years , months and days were 10, 3 and 20 respectively and the value of output was #4/15/2012# , the same as the initial input.