For Each Loop problem

Andrew, and over what period must the principal be re-paid fully, or in other words how many installments?

How do you want to show the result?

a vertical list of dates and amounts, or a horizontal list (row 9) whereby each column equals one calendar week?

In case you opt for the horizontal list, note that you have not provided dates for all columns needed. Do you want the coding to add these dates (in row 2) as well?

Try

Public Sub SchedulePayments()
     Dim lngNumberOfInstallments As Long
     Dim lngColumnNumber As Long
     Dim dblInstallment As Double
     
     With ThisWorkbook.Worksheets("Sheet1")
     '# calculate installment
          lngNumberOfInstallments = ((CInt(.Cells(5, "C").Value) * 52) / CInt(.Cells(7, "C").Value))
          dblInstallment = Val(.Cells(4, "C").Value) / lngNumberOfInstallments
     '# position installments on timeline
          For lngColumnNumber = 4 To (lngNumberOfInstallments * CInt(.Cells(7, "C").Value)) Step CInt(.Cells(7, "C").Value)
               .Cells(9, lngColumnNumber).Value = dblInstallment
          Next lngColumnNumber
     End With
End Sub

or

Public Sub SchedulePayments_alternative()
     Dim lngNumberOfInstallments As Long
     Dim lngColumnNumber As Long
     Dim dblLoanAmount As Double
     Dim dblInstallment As Double
     
     With ThisWorkbook.Worksheets("Sheet1")
     '# calculate installment
          dblLoanAmount = Val(.Cells(4, "C").Value)
          lngNumberOfInstallments = ((CInt(.Cells(5, "C").Value) * 52) / CInt(.Cells(7, "C").Value))
          dblInstallment = dblLoanAmount / lngNumberOfInstallments
     '# position installments on timeline
          lngColumnNumber = 4
          While dblLoanAmount > (dblInstallment)
               .Cells(9, lngColumnNumber).Value = dblInstallment
               dblLoanAmount = dblLoanAmount - dblInstallment
               lngColumnNumber = lngColumnNumber + CInt(.Cells(7, "C").Value)
          Wend
     End With
     
End Sub

whichever bit of code you find easier to work with

It is not, as I assumed cell (9,4) to be the date of the first instalment. To calculate the date of the first instalment you could use the following code

first_installment = DateAdd("ww",.Cells(6,"C").Value,Now())

the above code returns the date x weeks from now (in the example 52 weeks), depending on which date you have shown for the column headers, you may need to adjust for the day_of_the_week which can be retrieved usign the code below

day_of_week = Format(Now(),"w")

Using these two statements you can arrive at the 'date' for the first instalment, and using that date you can search for the column holding that date using

column = Application.Match(calculated_date, .Rows(1),0)