"Ruan" wrote...
....
So, I would have a formula as follows -
=IF(AND(Patient_Name<"",Admit_Date<""),Admit_Da te+30,"")

My question is, which direction is more efficient -
1) Creating formulas that are copied for 1000 rows or
2) Creating VBA code that only enters the result once an input has
been entered in the Admit Date column.
....

If you're really concerned with efficiency, you shouldn't be using
spreadsheets at all. A Tk frontend on a simple XML format would be much more
storage and speed efficient than anything involving Excel.

That said, there are ways to improve efficiency by *simplifying* formulas.
If the <"" tests in your formula are intended to check if the two
referenced cells are nonblank, you could replace your formula with

=IF(COUNTA(Patient_Name,Admit_Date)=2,Admit_Date+3 0,"")

The event handler alternative would require code to figure out which cells
should be used as patient name and admit date. Probably on the same row as
the changed cell. Then you have to have code to exit the event handler
quickly if you haven't entered the required info to fill in the other dates.
Presumably you don't want to fill in 30-Jan-1900 when you enter patient name
before entering admit date.

So you'd need something like

Private Sub Worksheet_Change(ByVal Target As Range)
Dim da As Variant, i As Long

If Target.Column < Evaluate("Admit_Date").Column Then Exit Sub

On Error GoTo CleanUp
Application.EnableEvents = False

da = Array(15, 30, 45, 60)

If Not (IsEmpty(Target.Value) Or IsEmpty(Target.Offset(0, _
Evaluate("Patient_Name").Column - Target.Column).Value)) Then

For i = LBound(da) To UBound(da)
Target.Offset(0, Evaluate("Admit_" & Format(da(i))).Column _
- Evaluate("Admit_Date").Column).Value = Target.Value + da(i)
Next i

End If

CleanUp:
Application.EnableEvents = True

End Sub


Spreadsheet formulas represent a functional programming language biased
towards rectangular data structures. VBA despite its object-oriented veneer
is a procedural language. If you think more readily in functional
programming constructs, use formulas. If you find it easier to thing
procedurally, use VBA. If the workbook would be used by others (and some day
maintained by others), use whatever is clearest (generally a handful of
formulas beats even the best written VBA for clarity for other maintainers).