The question was asked in order to provide the answer to what should be declared on the form (I'm filling in the employee IR56B's right now and it's an actual issue!). I think going through some previous threads where you had put the calculation down, it's possible an employee would be worse off if they declared a sub-10% housing so, as you note, the right thing to do is not declare it. (The employee in question has never looked at the tax rules and had no idea how they worked, they just "assumed" a housing allowance was a good thing.......)