You could select a range (B2:B7 for 20 to 30).

Then do Edit|fill|series
There's an option in there for linear.

Or you could click the Trend box and use Linear or Growth.

This does the a linear version for each step in code:

Option Explicit

Sub testme()
Dim TopCell As Range
Dim BotCell As Range
Dim FirstRow As Long
Dim myStep As Double

With ActiveSheet
FirstRow = 2

Set BotCell = .Cells(.Rows.Count, "B").End(xlUp)

Do
Set TopCell = BotCell.End(xlUp)

myStep = (BotCell.Value - TopCell.Value) _
/ (BotCell.Row - TopCell.Row)

With .Range(TopCell, BotCell)
.DataSeries Rowcol:=xlColumns, _
Type:=xlLinear, Date:=xlDay, Step:=myStep, _
Trend:=False
End With

Set BotCell = TopCell
If BotCell.Row <= FirstRow Then
Exit Do
End If
Loop
End With

End Sub

It does assume that you don't have any values in column B that are
adjacent--there always has to be a gap.

If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm

Triv wrote:

I have a list of data in which I would like to fill in the gaps. Is this
possiable?

I have age in years in A2 to A100 then data in colums in 5 year gaps (eg B2
has data then B7 then B12 etc) all incremental. I would like to fill in the
gaps belween giving me data B2, B3, B4... to B100.

How can I fill in the gaps whilst still making sure my 5 year results are
left.

Simple example below
age Result
45 20
46
47
48
49
50 30
51
52
53
54
55 50

Many Thanks for any help

--

Dave Peterson