If you execute transaction VF04 to process the billing due list and create invoices, an ALV list is shown. Here appearantly the column with “Billing Date” is shown twice.

Checking the field’s technical characteristics, it can be seen that the first column shows FKDAT, whereas the second one V_FKDAT:

What is here the difference?

The first column with the billing date FKDAT shows this date, which the system would use as default billing date, if no other entries are made by the user. In delivery related billing this is usually the post goods issue date, in order related invoicing the billing date entered in the sales order.

Now comparing this FKDAT billing date column with the second one of V_FKDAT, then the dates mostly are identical.

However if you enter at the start of transaction VF04 on the default tab a billing date:

Then in the ALV list, for V_FKDAT this default date is shown, whereas FKDAT remains the same:

Another functionality of V_FKDAT is that always the oldest billing date is shown in case of several items in the same sales order, which have different billing dates:

Then in VF04 the ALV list without entering a default billing date looks like this: