It's a least squares linear regression.
There's more info on FORECAST at http://support.microsoft.com/kb/828236
You may want to look at the LINEST function
http://support.microsoft.com/kb/828533 which gives more indications of the
quality of the correlation.

Yes, you can extrapolate as long as you like, but I would have no faith in
predicting results in that way (and 4 previous results is a very small
sample from which to draw any statistical conclusions).
Excel also has various random number generating functions which may be
equally useful.
--
David Biddulph

"RobertStanke" wrote in message
...
Just curious so I know what I am looking at when I see the results... do
you
know what logic Excel is using to determine the value that outputs? BTW,
I
tried it and it seems to be working. I am assuming I can do that for as
many
weeks as I want and get an indication of what the end of the year total
will
be, right?

"David Biddulph" wrote:

Yes, FORECAST would be OK if you believe in a linear best fit and
extrapolating.

If your game numbers 1 to 4 are in column A, & your distances in column
B,
then use =FORECAST(5,B1:B4,A1:A4)

You can, of course, also show this graphically by selecting the range
with
the game numbers & distances, Insert/ Chart/ XY (& choose an appropriate
sub-type). Finish the chart, then select the series, right-click/ Add
Trendline, and choose the option to extend forward by 1 unit.
--
David Biddulph

"RobertStanke" wrote in message
...
I thought I was using the right function command, but perhaps not. Here
is
my issue: I have a roster of football players who have stats set-up in
Excel.
I want to be able to, after a series of games already played, forecast
or
predict the what the outcome of the next game might be. For example:

A running back runs for 97 yards, 36 yards, 97 yards, and 102 yards in
the
first four games of the season. I want to forecast what he might rush
for
in
the 5th game. How do I do this in Excel?