Calculate values before end date - excel

Question

I'm quite new to VBA, and I'm trying to calculate the values before/equal to the end date requested to the user, but can't seem to figure it out.
14/03/2022 (Q1)
21/03/2022 (R1)
08 (Q2)
10 (R2)
40 (Q3)
20 (R3)
my goal is to process each existing row and return the sum on that specific row in column N:N.
so if the user says end date is 21/03 the total value for 2nd row should be 18 and 3rd row 60.
The code should summarize the values corresponding to each A:A column existing cells row. I mean, for the third row, the data will be summarized from the third row bellow the one keeping the reference dates.
Here is my code so far:
Sub test()
Dim WS As Worksheet
Set WS = Worksheets("Sheet1")
Const EARLIEST = #1/1/2000#
Dim till As Date
'On Error GoTo Errorhandler
till = CDate(Application.InputBox(Prompt:="Please enter the date to split the hrs (dd/mm/yyyy):", Type:=2))
If till = 0 Then Exit Sub
If till < EARLIEST Then
MsgBox "You need to insert a valid date dd/mm/yyyy"
Exit Sub
End If
'need to do more spotchecks as check if date exists in the file
ActiveSheet.Range("N1").Select
ActiveCell.FormulaR1C1 = "Total until " & till
Dim lr, lc, lc1 As Long
Dim sum As Long
lr = Range("Q" & Rows.Count).End(xlUp).Row
lc = Cells(2, Columns.Count).End(xlToLeft).Column
lc1 = Cells(1, Columns.Count).End(xlToLeft).Column
Set dates = WS.Range("Q1" & lc1)
For i = 2 To lr
If dates.Value <= till Then
sum = sum + Range("Q2" & lc)
Range("N" & i).Value = sum
End If
Next i
Columns("N:N").Select
Selection.Style = "Comma"
Selection.NumberFormat = _
"_ * #,##0.0_)_ ;_ * (#,##0.0)_ ;_ * ""-""??_)_ ;_ #_ "
Selection.NumberFormat = "_ * #,##0_)_ ;_ * (#,##0)_ ;_ * ""-""??_)_ ;_ #_ "
Columns("N:N").EntireColumn.autofit
'Errorhandler:
'MsgBox "You need to insert a valid date dd/mm/yyyy"
'Resume
End Sub

Answer 1

Please, try the next version:
Sub testProcessDate_All()
Dim WS As Worksheet: Set WS = Worksheets("Sheet1")
Const EARLIEST = #1/1/2000#
Dim till As Date
till = CDate(Application.InputBox(Prompt:="Please enter the date to split the hrs (dd/mm/yyyy)" & vbCrLf & _
"or select a cell containing a date in the first row:", Type:=2))
If till = 0 Then Exit Sub
If till < EARLIEST Then
MsgBox "You need to insert a valid date dd/mm/yyyy"
Exit Sub
End If
Dim lc1 As Long: lc1 = WS.Cells(1, WS.Columns.Count).End(xlToLeft).Column
Dim LatestDate As Date
LatestDate = WS.Cells(1, lc1).Value
If till > LatestDate Then MsgBox "The chosen date is larger than last available date...": Exit Sub
'ActiveSheet.Range("N:N").ClearContents 'to be cleared for the next time
WS.Range("N1").Value = "Total until " & till
Dim lr As Long, sum As Long, i As Long, j As Long
If WS.Range("A2").Value = "" Then MsgBox "No values in A:A to run the code...": Exit Sub
lr = WS.Range("A1").End(xlDown).Row 'the last row in A:A (for a table...)
For j = 2 To lr
For i = WS.Range("Q1").Column To lc1
If CDate(WS.Cells(1, i).Value) <= till Then
sum = sum + WS.Cells(j, i).Value
Else
Exit For
End If
Next i
WS.Range("N" & j).Value = sum: sum = 0
Next j
End Sub