When you reference cells in a formula and then use the AutoFill feature, Excel modifies the reference to cells relative to the newly filled cells. That means you can create a whole series of calculations simply by creating a single calculation and then filling cells with the formula. And if you need to use a single constant value in all the calculations, you can use an absolute reference to a cell instead of a relative reference.
To include a reference to the same cell in all the formulas, make the reference to the cell absolute instead of relative. Press the F4 key to switch from a relative to an absolute reference.
"Cell References, Formulas, and Functions" for information about the difference between relative and absolute references.
"Copy Content to Adjacent Cells" for information about using the Fill handle to copy the contents of a cell instead of creating a series.