That online calculator is a crude tool which is not designed to cope with all possible sets of circumstances, and certainly is not designed to cope with any changes.
The sum the online calculator comes up with, in my experiene, is often not the same sum you find on your award, either
The online calculator can't deal with projected earnings properly, but only with looking at what you've earned previously, which is no big help when you or your partner suddenly finds themselves without a job in April, but had a reasonable income previously.
It's a shite tool, in my opinion, but maybe I'm just a bit thick, and I shouldn't have found the last 6 months so stressful, because it's all so easy. 