Calculating After Tax Returns - Real Estate Finance

So I'm essentially moving from East Coast to London and switching up jobs in the process so I've been interviewing quite actively for acquisitions roles in London for the last month. I've had a few case studies and nothing is particularly out the order (compared to the U.S. process), but I keep getting asked to calculate after-tax return from nearly all companies, which new to me.. (and strange, isn't this why you have fund accountants?)

In previous role, when we were UW, we generally looked at deal level returns (like IRR/EMx/CoC etc.), and never went beyond the waterfall structure so I would really appreciate insights on this from someone who know this better than me! 

For example, if I'm given a Corporate Income Tax of 20%, which line item do I use to calculate the additional CIT? Initially, I thought it would make sense to use Cash Flow to Equity Investors, but then I remembered that items such as Interest Payments are tax deductible so I'm really confused... 

Really would appreciate any insight you might have!