Reckon has no calculator in it. If I have paid two invoices in one day to one supplier, I have to "add row" and only then will Reckon add them up. I should be able to type in, say $10 + $10 and Reckon can work out that the total is $20. It's a common feature these days and in fact always has been.
This idea already exists. Merging with idea RKN1-I-19