Question on child benefit entitlement

Hi,

I'm just a bit confused about how the calculator works which looks at how much you are entitled to claim for a child. Basically, myself and my partner are expecting a baby in December and I was looking to see what we are entitled to claim while she is on maternity.

Our combined annual salary would be somewhere around the 35k mark, however, when she is on maternity that would obviously be significantly reduced. But looking at the calculator it asks what she earned for the previous tax year. Why is this relevant? Surely being on maternity pay is the main factor as that is the reason why we would need the help in the first place.

The calculator came back with us not being entitled to anything, which I find shocking. We are home owners and both on ok wages but like I said that will be reduced shortly. I'm just looking for a bit of advice on how the process works. Surely we have to be entitled to something? I'm just confused as to why we have to say how much we earned last year, when it's what we will be earning at the time that is the problem.

Any help would be excellent.