Before you open a line, before your first parked paycheck, before any of it, you need one number: how much money is actually left over in a normal month. Not what you think is left over. What's actually left. Every calculation in this whole strategy runs on that number, and most people I talk to don't know theirs.
Your bank balance won't tell you. A balance is a snapshot, and it lies in both directions. Flush right after payday, grim right before the insurance bill hits. The number you want is flow. Income in, minus everything out, averaged over enough months to catch the lumpy stuff.
Here's the honest way to get it. Pull 90 days of statements, every account and every card, and total what came in and what went out. Then hunt down the once-a-year items that didn't happen to land in your window. Car insurance, property taxes, Christmas, the vet. Divide those by twelve and subtract that share too. The number that survives all of this is your real monthly surplus, and it's almost always smaller than the number you'd have guessed. Mine was, the first time I did this exercise.
That number decides everything downstream. It tells you how fast a parked line actually pays down. It sizes your first chunk, because a chunk your surplus can bury in a few months is a good chunk, and a bigger one is a trap. Run the strategy on a guessed surplus and the timeline stretches, the interest math sours, and you'll conclude the strategy failed when the input was what failed.
If the exercise turns up a surplus near zero, that's not a verdict on you. It's a to-do list. Finding the leak is a solvable problem, and it's covered from the consumer side at Oregon Cash Flow Pro. Once your real number is in hand, the How It Works page shows you what to do with it.