The only compound interest calculator that shows you real purchasing power — not just the nominal number that ignores inflation.
A 7% annual return sounds great until you account for 3% inflation — your real return is only 4%. Over 30 years, $100k grows to $761k nominally, but in today's dollars it's only worth $314k. This calculator shows both figures so you can plan realistically.
Divide 72 by your interest rate to estimate how long it takes to double your money. At 7%, money doubles roughly every 10 years. At 10%, every 7.2 years. Starting early matters enormously — $10k invested at 25 becomes nearly $217k by 65 at 8%; the same $10k invested at 35 becomes only $100k.
Once you see long-term compounding clearly, the practical next move is budgeting, savings rate planning, and personal FIRE projections.
Compound growth becomes more useful when it is tied to a real monthly savings plan, spending discipline, and an explicit independence target.