Try this, you haven't siad where you want the results so a have output it to columns j and K
Sub test()
lastrow = Cells(Rows.Count, "A").End(xlUp).Row
inarr = Range(Cells(1, 1), Cells(lastrow, 4))
Dim Monarr(1 To 12, 1 To 2) As Variant
Monarr(1, 1) = "January"
Monarr(2, 1) = "February"
Monarr(3, 1) = "March"
Monarr(4, 1) = "April"
Monarr(5, 1) = "May"
Monarr(6, 1) = "June"
Monarr(7, 1) = "July"
Monarr(8, 1) = "August"
Monarr(9, 1) = "September"
Monarr(10, 1) = "October"
Monarr(11, 1) = "November"
Monarr(12, 1) = "December"
For k = 1 To 12
Monarr(k, 2) = 0
Next k
cnt = 0
cntlim = 15
person = 0
For i = 2 To lastrow
If inarr(i, 1) <> person Then
' new person
cnt = 0
cntlim = 15
person = inarr(i, 1)
End If
cnt = cnt + inarr(i, 3)
If cnt >= cntlim Then
cntlim = cntlim + 5
For k = 1 To 12
If inarr(i, 2) = Monarr(k, 1) Then
Monarr(k, 2) = Monarr(k, 2) + 1
End If
Next k
End If
Next i
Range(Cells(1, 10), Cells(12, 11)) = Monarr
End Sub