TREND function
This article describes the formula syntax and usage of the TREND function in Microsoft Excel.
Description
Returns values along a linear trend. Fits a straight line (using the method of least squares) to the arrays known_y's and known_x's. Returns the yvalues along that line for the array of new_x's that you specify.
Syntax
TREND(known_y's, [known_x's], [new_x's], [const])
The TREND function syntax has the following arguments:

Known_y's Required. The set of yvalues you already know in the relationship y = mx + b.

If the array known_y's is in a single column, then each column of known_x's is interpreted as a separate variable.

If the array known_y's is in a single row, then each row of known_x's is interpreted as a separate variable.


Known_x's Required. An optional set of xvalues that you may already know in the relationship y = mx + b.

The array known_x's can include one or more sets of variables. If only one variable is used, known_y's and known_x's can be ranges of any shape, as long as they have equal dimensions. If more than one variable is used, known_y's must be a vector (that is, a range with a height of one row or a width of one column).

If known_x's is omitted, it is assumed to be the array {1,2,3,...} that is the same size as known_y's.


New_x's Required. New xvalues for which you want TREND to return corresponding yvalues.

New_x's must include a column (or row) for each independent variable, just as known_x's does. So, if known_y's is in a single column, known_x's and new_x's must have the same number of columns. If known_y's is in a single row, known_x's and new_x's must have the same number of rows.

If you omit new_x's, it is assumed to be the same as known_x's.

If you omit both known_x's and new_x's, they are assumed to be the array {1,2,3,...} that is the same size as known_y's.


Const Optional. A logical value specifying whether to force the constant b to equal 0.

If const is TRUE or omitted, b is calculated normally.

If const is FALSE, b is set equal to 0 (zero), and the mvalues are adjusted so that y = mx.

Remarks

For information about how Microsoft Excel fits a line to data, see LINEST.

You can use TREND for polynomial curve fitting by regressing against the same variable raised to different powers. For example, suppose column A contains yvalues and column B contains xvalues. You can enter x^2 in column C, x^3 in column D, and so on, and then regress columns B through D against column A.

Formulas that return arrays must be entered as array formulas.
Note In Excel Online you cannot create array formulas. 
When entering an array constant for an argument such as known_x's, use commas to separate values in the same row and semicolons to separate rows.
Example
Copy the example data in the following table, and paste it in cell A1 of a new Excel worksheet. For formulas to show results, select them, press F2, and then press Enter. If you need to, you can adjust the column widths to see all the data.
Month 
Cost 
Formula (Corresponding Cost) 
Live Result 
1 
$133,890 
=TREND(A2:A13,B2:B13) 
$133,953 
2 
$135,000 
$134,972 

3 
$135,790 
$135,990 

4 
$137,300 
$137,008 

5 
$138,130 
$138,026 

6 
$139,100 
$139,044 

7 
$139,900 
$140,062 

8 
$141,120 
$141,081 

9 
$141,890 
$142,099 

10 
$143,230 
$143,117 

11 
$144,000 
$144,135 

12 
$145,290 
$145,153 

Month 
Formula (Predicted Cost) 

Live Result 
13 
=TREND(B2:B13,A2:A13,A15:A19) 
$146,172 

14 
$147,190 

15 
$148,208 

16 
$149,226 

17 
$150,244 

In the Live Result column, the ranges D2:D13 and D15:D19 each contain one formula that is used for all cells in the range. Enter the formula =TREND(A2:A13,B2:B13) in D2:D13 with all its cells selected and then press CTRL+SHIFT+Enter to enter it as an array formula. 