When you use the AutoFill handle in Excel, as well as copying your formula it also copies your formatting.
In the example shown here, the worksheet was already formatted with a border around the table. When you use the AutoFill handle to replicate the formula in cell C3 down through range C4 to C11, a little symbol shows when you leave go of the mouse. If you ignore this symbol and move to a different cell, you will find that the bottom border in cell C11 is no longer there.
If however, you open up the dropdown next to the symbol, you will find you have three options:
If you select the third of these options, Fill Without Formatting, the border will remain and your formula will be correctly copied down.
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