Hi, mumagain – Maybe try refreshing the calculator page: before entering any details, click on the small, curving, circular arrow symbol at the right of the page’s individual identity – which address is called the URL, I think – in the address box at the top of the page, i.e. besides the words:

http://thefastdiet.co.uk/how-many-calories-on-a-non-fast-day/

Once it re-boots, have another go at putting in your details. The calculator just worked fine for me. Hope it does for you too.