Type the formula in the first cell of the column
Press Enter
Select the cell with the formula
Drag the fill handle down the column
Double-click the fill handle to auto-fill adjacent rows
Copy the formula cell
Select the entire target range or column
Paste the formula
Use Ctrl+D to fill down selected cells
Convert the range to a table so formulas auto-fill in new rows
Use the column name in an Excel table formula for automatic propagation