Its just an exercise in curiosity.
Essentially he wants to see if the interest paid over the mortgage has been eroded away by the increase in house price e.g.
- Paid £100,000 for house in 1995
- Use the calculator in his link to estimate what £100,000 is now equal to in today's money - £198,000 (rounded from that calculator)
- House is now "worth" £300,000 today (price if you were to sell it today)
- £300,000 less £198,000 (value of house currently less value of house in 1995 adjusted for inflation) = £102,000 "gained value"
- Total Paid in Deposit+Mortgage Payments = £250,000 (so £100,000 for house (point 1) and therefore £150,000 paid in interest)
- £150,000 interest paid less £102,000 "gained value" = £48,000 in interest paid (comparatively)
At least I think that's what he is trying to see.
I still don't get the point being made. Isn't it obvious that the house prices increase effectively erodes away the interest paid?
Buying outright will always be the better option, unless you can guarantee a better return on your money than the interest being paid.