Once the line of credit is the hub, the temptation is to run everything through it. Groceries, the mortgage, the tax bill, the kid's braces. Most of that is fine. A few categories cost you more to route than they save.

Start with the fee. A HELOC check or an ACH transfer is usually free. A cash advance against a credit card line is not, and neither is a balance transfer with a 3% up-front charge. Paying a $6,000 tax bill through a processor that adds 1.85% costs you $111 before you've saved a dime of interest. Run the fee against what the money saves during the weeks it's outstanding. Sometimes it clears. Often it doesn't.

Then reversibility. Anything you might need to dispute belongs on a credit card. Card networks have a chargeback process with real teeth. A HELOC draw sent to a contractor who disappears is a loan you now owe with nobody left to argue with. Contractors, deposits on services, anything bought from a business you've never used, all of that goes on the card, and the card gets paid from the line of credit at the end of the cycle.

Predictable expenses are the best fit. The mortgage, insurance, utilities, groceries, fuel. They repeat, you can forecast them, and forecasting is what lets you size a chunk without guessing. Irregular large purchases are fine too, as long as you know what the payback looks like before the money moves.

What doesn't belong is anything that pushes the balance past your comfort ceiling. The rule that keeps this safe is available room, and a $9,000 vacation that eats the room you were holding for a furnace turns a strategy into exposure. The vacation isn't the problem. The vacation on top of a balance already sitting at 70% of the limit is.

Business expenses need their own line of credit. Mixing them with household spending on one account makes the bookkeeping ugly at tax time and can muddy the deductibility of the interest. A separate business line costs a little more in setup and saves an accountant's hourly rate in April. Your CPA should be the one who confirms how the interest gets traced.

One more that surprises people: retirement contributions. Borrowing at 8% to fund an account you can't touch for twenty years is a different transaction from routing a mortgage payment through a balance that gets cleared next payday. The first is leverage on a long horizon. The second is cash flow management. Keep them separate in your head, and mostly, keep them separate in your accounts.