The two ledgers
Nominal dollars are what the statement shows; real dollars are what they buy. At 3% inflation, a 7% nominal return is a 4% real return — still excellent, but a $500k projection in 30 years is a ~$206k lifestyle in today's terms. Planning exclusively in nominal dollars is how "millionaire by 60" becomes an underfunded retirement.
Where to use which
Track progress (and compare against your deposits) in nominal dollars — that is the scoreboard. Set goals and make decisions in real dollars — that is the game. The lump-sum and monthly calculators here show both columns precisely so the two ledgers stop being confused.
The assets that fight back
Equities and real estate have historically outpaced inflation over long horizons (their earnings reprice); cash and most bonds roughly trade places with it. This is the actual argument for stock-heavy allocations at long horizons — not risk tolerance aesthetics, but the specific job of outrunning the silent counterparty.