I came up with the below formula which mimics the Excel Forecast formula.

Linear Regression Forecast Equation: =((((SUM(y2-y1) + (y2n-y1n)) /
(SUM(x2-x1))*(x2(n+1)-x1(n-1)))+y(n-1))-(x2(n-1)-x2(n-2)));€¦..n=last point;
y=variable points; x = constants

Example (put it in Excel and compare it):
Example Details: For a year...you have 3 known data points (must have at
least 2). Place the formula in the Variable Y column and keep increasing the
knwon X months. The formual will perform a linear regression forecast using
the previous data points,...plotint the future data points.

Header----------- Variable Y (Actual Data) Known X (Months)
row 1 ------------ 2 1
row 2 ------------ 4 2
row 3 ------------ 6 3
row 4 ------------ equation 1 below 4
row 5 ------------ equation 2 below 5
row 6 ------------ equation 3 below 6
row 7 ------------ equation 4 below 7
8

equation 1:
=(((((A2-A1)+((A3-A2)*2))/((B2-B1)+(B3-B2)+(B4-B3))*(B5-B3))+A3)-(A3-A2))

equation 2:
=(((((A2-A1)+(A3-A2)+((A4-A3)*2))/((B2-B1)+(B3-B2)+(B4-B3)+(B5-B4))*(B6-B4))+A4)-(A4-A3))

equation 3:
=(((((A2-A1)+(A3-A2)+(A4-A3)+((A5-A4)*2))/((B2-B1)+(B3-B2)+(B4-B3)+(B5-B4)+(B6-B5))*(B7-B5))+A5)-(A5-A4))

equation 3:
=(((((A2-A1)+(A3-A2)+(A4-A3)+(A5-A4)+((A6-A5)*2))/((B2-B1)+(B3-B2)+(B4-B3)+(B5-B4)+(B6-B5)+(B7-B6))*(B8-B6))+A6)-(A6-A5))

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"Sumit Kumar" wrote:

Hello ,
I need to use forecast formula outside excel.
I explored the forecast method in excel and could not figure out the
formula. X(Bar) & Y(Bar) signify what ?

Thanks in advance

"Rodney M" wrote:

No,...Excel gives me the formual, but I don't really know how to decode that
algebraic formula enough to come up with a forcasted number. I may have
phased my question incorrectly though.
I think that we figured out the answer though:
Jan(1) - 3; Feb(2) - 6; March(3) - 9...
Plugging the number into this equation will give you the next forcasted
number (given any two months): y3 = (((y2-y1)/(x2-x1))*(x3-x1))+y1

Example: Third month sales (y3) equals (2nd month sales (y2) minus 1st month
sales (y1) divided by 2nd month (x2) minus 1st month (x1)) times (3rd month
(x3) minus 1st month (x1)) plus 1st month sales (y1)

Thanks

"Dave F" wrote:

Haven't you answered your own question here?

Dave
--
A hint to posters: Specific, detailed questions are more likely to be
answered than questions that provide no detail about your problem.


"Rodney M" wrote:

Hello All,
Background: I am trying to figure out how to project my sales numbers for
the year, given a few monthly entries. In Excel I can use the Forcast
function, but I am working in MS Access.

Question: Does anyone know how to break down the way that the Excel Forcast
function predicts it's next value given previous values?

Example: Jan - 2; Feb - 4; March - 6. The rest of the year's numbers should
project to....Apr - 8; May - 10; June - 12; July - 14 ...etc.

The equation for FORECAST is a+bx, whe
a = y - bx
AND
b = (sum(x-x)(y-y)/sum(x-x)^2)
AND
where x and y are the sameple means AVERAGE(known_x's) and AVERAGE(known_y's)

Thanks for any assistance

Rodney