It has just come to my notice that this year I missed my half millionth Birthhour, which was also my 30 millionth Birthminute. Luckily I still have plenty of time to prepare for my 2 billionth Birthsecond.
To avoid missing these significant occasions download Anniversaries.zip and calculate to the second the exact anniversary from any specified date and time.
Anniversaries - Screen shot
Newton Excel Bach, not (just) an Excel Blog 
=DateAfter() is new to me (and to excel 2007) I assume it is VBA?
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Nick – yes there are two UDFs included in the download; =DateAfter() and =Phi().
Here’s the code:
Function Phi() As Double
Phi = 1.61803398874989
End Function
Function DateAfter(DateFrom As Double, Period As Double, Optional TUnit As String) As Variant
Dim TFactor As Double, Yearinc As Long, Monthinc As Long, Dayinc As Double, YearLength As Long
If IsMissing(TUnit) = True Then
TFactor = 1
Else
TUnit = LCase(TUnit)
Select Case TUnit
Case “seconds”
TFactor = 1# / (24# * 3600#)
Case “minutes”
TFactor = 1 / (24 * 60)
Case “hours”
TFactor = 1 / (24)
Case “days”
TFactor = 1
Case “weeks”
TFactor = 7
Case “months”
TFactor = -1
Case “years”
TFactor = -2
Case Else
DateAfter = “Invalid Time Unit”
Exit Function
End Select
End If
If TFactor = -1 Then
Yearinc = Int(Period / 12)
Monthinc = Int(Period – Yearinc * 12)
Dayinc = (Period – Int(Period)) * 365 / 12
DateAfter = DateSerial(Year(DateFrom) + Yearinc, Month(DateFrom) + Monthinc, (DateFrom – Int(DateFrom)) + Dayinc)
ElseIf TFactor = -2 Then
Yearinc = Int(Period)
DateAfter = DateSerial(Year(DateFrom) + Yearinc, Month(DateFrom), Day(DateFrom))
YearLength = DateSerial(Year(DateFrom) + Yearinc + 1, Month(DateFrom), Day(DateFrom)) – DateAfter
Dayinc = (Period – Int(Period)) * YearLength
DateAfter = DateAfter + Dayinc + (DateFrom – Int(DateFrom))
Else
DateAfter = DateFrom + Period * TFactor
End If
End Function
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