I am trying to do a simple cashflow.

Coloumn A on my spreadsheet contains a list of dates when money is either
recieved or paid out. Every two weeks I get a payment from X for £100
starting on coloum A2. Coloumn a5 is the next bi weekly payment of £100 and
the formula entered at a5 is, therefore, a2+14 (i.e. the date 2 weeks from
a2). The next payment from x is at cell a12 and the formula at a12 will be
a5+14 and I continue in the same way whenver money is recieved from X.

I have tried at the end of my cashflow (say coloumn a200) to put the first
date payment is recieved from x and then at coloum a201 the formula a200 +14
and then copy and paste a201 for another 9 coloumns down which gives me the
date every two weeks that payment is due from x. I then sorted my cashflow
according to coloumn a which obviously messed up the dates for x payment
(i.e. the previous date is taken from the cell immediately before as opposed
to the cell on which last payment is due/ was made).

Is there any way to put the date every two weeks into my spreadsheet easily
(rather than calculating using a calendar the date every two weeks).
Additionally, if I insert a row and that changes the cell number of the
original date, is there any way to still be able to sort my cashflow by date?

Here's hoping and thanks in advance.