I do this kind of calculation all the time. It's great fun.

A client of mine who works as a Financial Advisor told me about a client of his who won a big number in the lottery when she was in her sixties. She was persuaded to buy a letting property portfolio for tax reasons, and, he said, she woke up every morning worrying that she didn't have enough to pay the mortgages.

He said that she would have been better off putting the money in the bank and enjoying it.