The problem I have with simple calculators like this is that there's a lot of details that get left out, some of which matter, as you've pointed out.
Personally when I look at my income vs. what I'm saving and what I'm spending, I include my employer match for my 401k and ESOP as income. I also include SS withholding as tax since I won't be paying that once I retire. When I do that I find that 26% of my income goes to taxes, 35% goes towards savings and the remaining 39% goes towards current spending. Of the current spending about 40% goes towards rent. We don't own real estate so the OP's questions is easily answered for me. What does matter to me is that when SO and I retire we will be moving somewhere cheaper. We will buy a home with cash and our rent expense will disappear. So, in order to maintain my current lifestyle, my retirement income need will be approximately 24% of my current (all in including employer savings matches) earnings, plus whatever additional costs homeownership will entail, plus whatever additional health insurance/healthcare costs we will have.
A simple "you need to have saved X by this point in your life" calculation doesn't seem sufficient for me because details matter.