Greetings, I cannot seem to work out what my syntax error is in the following formula:

IF(B1="","",IF(AND(B1<A1,B1>A1-90),A1+360,B1+360))

Column A refers to a date something is due, column B the date it was completed.
The new due date is the calculation that I am trying to formulate.

Can anyone help? Grateful for any assistance as always!

Rgds
Harry