Use a Calculator.
It's just so silly that people want to depend on software to do the things your calculator will do. If you use software YOU have to fill in the numbers so why can't you just use a calculator? If you're worried about speed.... it only takes a few seconds longer. Honestly, if you don't know how to do it like this, you probably shouldn't be in business anyway... it's not going to work out for ya.
I started my 1st business in 1995 and have never even thought about using any software for something like this. I think the major reason is because I'm not a 'template' kind of guy. I like doing things my way and not following what things tell me to do. It's almost as though some people need a 'boss' to tell/show them what to do so they use software. You are your own boss, don't depend on software to tell you what to do.
If you are looking for a kind of all in one type of thing.... schedule/bids/workers/supplies, I can understand using software for something like that. But to use software to get a number for YOU that a calculator will do..... silly.