How it works
Each period the calculator takes your withdrawal out of the balance first, then credits the assumed return on whatever is left. That ordering matters: it is how an SWP mandate actually executes, and it is the more conservative of the two possible conventions.
The result hinges on one comparison. If your withdrawal is smaller than the growth the remaining balance earns, the corpus keeps rising even while you draw from it. If it is larger, every period eats a little capital, and the erosion accelerates because the shrinking balance earns less.
More detail
The calculator reports the withdrawal that would leave your capital exactly flat, so you can see which side of that line you are on rather than inferring it from the balance chart.
When the corpus does run out, the final withdrawal is whatever was left rather than the full amount — the schedule shows the partial payment instead of pretending a full one happened.
To see how much purchasing power a flat withdrawal loses over the period, use the inflation calculator.
To see how the same corpus would grow if you took nothing out, use the lumpsum calculator.