From obliviousinvestor.com/whats-the…

if I knew that I wanted to have $10,000 of spending power 10 years from now, a TIPS fund doesn’t achieve that goal for me, because I don’t know what the fund will be worth 10 years from now.

So far the only way to guarantee a specific “spending power” at a specific date in the future used to be to buy a TIPS bond rather than a TIPS bond fund. But now Blackrock offers a suite of Target Maturity TIPS ETFs but they currently have offerings only for a max of 10 years www.ishares.com/us/strate…

To understand this better, its good to understand the concept of Real Yield vs Nominal Yield