The use of LINEST for this purpose has already been discussed.
Alternately, David Braden has posted VBA code to extract the
coefficients directly from the chart into cells

http://groups.google.com/groups?selm....microsoft.com

The advantage of using the chart coefficients (either manually or via
Braden's code) is that pre-2003 LINEST uses a numerically poor algorithm
that can give inaccurate results with some data sets. The chart
trendline (extracted by Braden's code) is much better numerically,
provided you format the equation to display to full precision
(scientific notation with 14 decimal places).

Jerry

Ken Hardman wrote:

Using Charts to ploy trend lines, there is an option to display a polynomial
curve fit of the data on the chart. Is there a way to extract the
coefficients of the curve for further analysis in the spreadsheet?