A projection is a scenario, not a prediction
Calculators apply a constant rate month after month. Real markets deliver an uneven sequence with long flat periods and sharp drawdowns. Two portfolios with the same average return can end very differently depending on when the bad years arrive, which matters most when you are withdrawing rather than accumulating.
The useful way to read any projected corpus is as one branch of a range: if returns are around this level, here is roughly where you land.
Past CAGR describes history
Compound annual growth rate smooths a start and end value into one annualised number. It is excellent for comparing what actually happened across different assets and periods, and misleading if you paste it into a projection as if it will repeat. Change the start or end date by a year and the same investment can show a very different CAGR.
Nominal versus real
A projection that shows twelve per cent growth while prices rise six per cent a year has produced roughly six per cent of extra purchasing power, not twelve. For any goal more than a few years away — retirement, education, a home — inflate the goal's cost as well as the corpus, otherwise you are comparing a future number to a present-day price.
A practical routine
Run the projection three times: at a pessimistic rate, at a moderate rate, and at an optimistic one. Plan your contributions around the pessimistic case and treat the optimistic case as upside. Then check the moderate case against the inflated cost of the goal. If only the optimistic case reaches the goal, the plan needs more contribution or more time, not a higher assumption.