Inflation is the slow rise in prices over time, and it works in two directions at once: the things you buy get more expensive, and the cash you hold buys less. Neither shift is dramatic year to year, which is exactly what makes inflation easy to underestimate.
TL;DR — Enter an amount, a rate and a number of years in the inflation calculator to see future cost and shrinking buying power.
Two sides of the same coin
Inflation can be viewed from either end. Future cost asks what a basket of goods that costs $100 today will cost in 20 years — at 3% inflation, about $181. Buying power asks the reverse: what will today’s $100 be worth in 20 years’ purchasing terms — about $55. Both describe the same force; which framing you use depends on whether you are thinking about prices or savings.
Why idle cash is risky
The most important lesson is what inflation does to money sitting still. If your savings earn less than the inflation rate, their real value shrinks every year even though the balance on the statement never changes. A savings account paying 1% during 3% inflation is quietly losing about 2% of its buying power a year. This is the core argument for investing money you will not need soon, rather than letting it sit.
Planning around it
For long-term goals like retirement, inflation means a future sum buys less than the same amount today — so a target that sounds comfortable now may fall short later. Build a cushion for it. Run different rates and time spans in the inflation calculator to see how much buying power a given amount loses over the years that matter to you.