Calculations always wrong?

[Stevie]

I'm writing an app which is kind of a small payroll system that calculates NI but not tax. I've just got round to calculating the NI from equations that have been given to me by the tax office. The problem is my result is always 5p less than it should be. Can anybody see why??

curPercent = 10
curUEL = 27820
curEmpThreshold = 3952

Dim rsNI As ADODB.Recordset
Dim curGrossPay As Currency
Dim curEmpThreshold As Currency
Dim curUEL As Currency
Dim curPercent As Currency
Dim curCalc1 As Currency
Dim curCalc2 As Currency
Dim curResult As Currency

  ' Get NI Data from DB
  Set rsNI = New ADODB.Recordset
  rsNI.CursorType = adOpenForwardOnly
  rsNI.Open "National_Insurance", conCrowd, , , adCmdTable

  If not rsNI.EOF Then
  
    curGrossPay = CCur(txtGross.Text)
    curEmpThreshold = CCur(rsNI!NEL_Annual)
    curUEL = CCur(rsNI!UEL_Annual)
    curPercent = CCur(rsNI!Employee_Rate)
  
  End If

  rsNI.Close
  Set rsNI = Nothing

  ' Calculate Employee Contribution
  curCalc1 = curEmpThreshold / 52

  ' As pay period is 1, round down to whole pounds
  curCalc1 = Fix(curCalc1)

  curCalc1 = curGrossPay - curCalc1

  If curCalc1 <= 0 Then

    ' No NI Contribution
    Exit Sub

  End If
     
  curCalc2 = curUEL / 52
  
  ' Round up to whole pounds
    
  curCalc2 = Format(curCalc2, "######.##")
  
  If InStr(CStr(curCalc2), ".") <> 0 Then
  
    ' Not a whole pound, Round up
    curCalc2 = Fix(curCalc2)
    curCalc2 = curCalc2 + 1
  
  End If
  
  curCalc2 = curGrossPay - curCalc2

  ' If negative treat as zero
  If curCalc2 < 0 Then curCalc2 = 0

  curResult = ((curCalc1 - curCalc2) / 100) * curPercent

Sample results :

Gross : 280 Result : 20.45 I Get : 20.40
Gross : 310 Result : 23.45 I Get : 23.40
Gross : 325 Result : 24.95 I Get : 24.90
Gross : 400 Result : 32.45 I Get : 32.40

Any help will be greeted with open arms!!!

[FireBeast]

make sure your calculation are done with more than 2 decimals places, and don't round up or down until the very end.

hope this helps

FireBeast

[Stevie]

Cheers for the input, but there are rules to when (in the calculation) you are supposed to round. Thanks anyway.

Anyway I have just found out what was wrong. Nothing!
The bleeding NI tables are incorrect and have always been out by about 5p every year. Someone could have let me know that before I started checking all my results against them!!