What today's dollars will buy tomorrow, and what tomorrow's bills will cost — the quiet tax on cash.
US CPI has averaged ~2.6%/yr over the last 30 years, ~3.8% over the last 5.
A savings yield or conservative portfolio return, to show what beating (or just matching) inflation looks like.
This inflation calculator translates between today's and tomorrow's dollars, showing how much purchasing power a sum loses over time and what a given expense will cost in the future. It makes the hidden tax on cash easy to see.
Inflation raises prices, so the same dollar buys less each year. Cash that earns less than the inflation rate quietly loses real value.
It is what your money can actually buy. $100 today and $100 in twenty years are the same number but very different amounts of goods and services.
Holding assets that tend to outpace inflation — stocks, real estate, or inflation-protected bonds — helps preserve purchasing power better than idle cash.