Linear interpolation or other? If other, then more information is needed.

If the known data is contiguous, with the points to be interpolated
elsewhere on the sheet, you could use the FORECAST() function for linear
interpolation. If you want actual and interpolated data all together in
one array, then you will have to program the formula manually.

For linear interpolation, this is not difficult. For concreteness,
suppose dates are in column A with values in column B, and that B2 is to
be interpolated for A2 from A1:B1 and A3:B3. You can linearly
interpolate with
=B1+(A2-A1)*(B3-B1)/(A3-A1)
in B2. Copy/paste the formula into other cells with missing values,
(provided that you don't have 2 missing values in a row).

Jerry

Rocket Rod wrote:

Is there a way to automatically interpolate missing data between data points
in a spreadsheet
eg there might be a list of sequentail dates and a value against each one
but there might be 4 values missing.
By selecting the cells before and after teh missing 4, and choose a funtion
of interpolate, it automatically determines theer are 4 missing, theerfore
divides teh difference by 5 and adds that to each of the cells in turn -
filling in teh blanks.

Perhaps could be enhanced with options of moving average to calculate teh
next point