During the draw period, most HELOCs bill you interest only. On a $40,000 balance at 8%, that's about $267 a month, and the statement calls it your minimum payment due.
Pay exactly that every month and the balance stays $40,000 forever. You've rented the money. The statement isn't lying to you, it just isn't a payoff plan, and the difference matters because the draw period ends.
When it does, usually at ten years, the loan converts to amortizing over the remaining term. That same $40,000 over fifteen years at 8% is about $382 a month, and if your line of credit converts over ten years it's roughly $485. Households that budgeted around $267 get a payment that nearly doubles on a schedule they agreed to a decade earlier.
In a chunking strategy this is less of a problem, because the point of Dynamic Banking is that the balance is falling every month. The risk shows up when the payback stalls. Income drops, spending creeps, the balance stops moving, and the interest-only payment makes the stall comfortable enough that nobody notices for two years.
There's a second version of this on cards. A credit card minimum is usually 1% to 2% of the balance plus interest, which does amortize, just over decades. Both statements are showing you the smallest legal payment, not a plan, and both leave the arithmetic to you.
So use the interest-only floor as a diagnostic. If the amount you actually paid last month equals the minimum, your payback is parked. Three months of that in a row means something in the household budget changed and it's time to go find it.
Find your conversion date. It's on the original HELOC agreement, and most people have never looked it up. Knowing you have six years left instead of an open-ended arrangement changes how aggressively you'd size the next chunk.