IF Statment - Carry common part of IF Statment for entire column

Hello,

Here is what I have.

In E2 I have a date.
In AK1 I have the following =TODAY () - Will always populate with the current date.

In AK2 I have and IF Statment:

=(F2="",AK1-E2,O)

So if F2 is blank ... AK2 will display the numbers of days F2 has been blank. If it is not blank it will return a 0.

However when I go and copy the IF statment down the column of AK3 : .... The AK1 changes to AK3, AK4 etc ...

I need it to stay as AK1 considering that is where todays date will always be.

Thoughts ?

Thanks in Advance.

Maybe like this???

$AK$1