Here's a case study I built on the whiteboard. A household earns $5,000 a month and spends $4,000, so it has $1,000 of monthly cash flow. It owes $340,000. There's a credit card at 18% with a $140 payment, another card at 14% with a $5,000 balance and a $75 payment, a $28,000 car loan at 4% with a $360 payment, and a $300,000 mortgage at 4% with a $1,432 payment. The line of credit has a $15,000 limit at 6.25%.
The first move is a big chunk, because the cards cost far more than the line of credit. About $12,000 goes onto both cards at once and clears them. That frees $215 of monthly payments, so cash flow rises from $1,000 to $1,215. Twelve thousand of a $15,000 limit leaves $3,000 of room, which means the household is never at the edge of the line of credit. Paychecks go into the line of credit and bills come out of it, and a rewards card pays the monthly expenses and gets cleared each month.
The balance on the line of credit then falls by the monthly cash flow: roughly $10,785 after month one, $9,570 after month two, and $4,710 by month six. Once the balance drops under $5,000, the household throws another chunk at a debt.
The next targets are different. The car and the mortgage both cost 4%, which is below the 6.25% line. So the plan changes. I use $4,000 chunks, not giant ones, to keep the line of credit balance low. The first one goes to the car at month seven. The car loan was on a 45-month schedule, and it's paid off in month 24. After that, cash flow rises by $360, and about $1,575 a month goes toward the mortgage.
Here's what comes out. The mortgage is gone in 141 months, or 11.75 years, instead of 30. The mortgage interest paid is about $83,700, which is $131,900 less than the original schedule. The car loan saves about $1,386. Across everything, the household saves roughly $133,000 in interest and pays under $85,000. The interest on the line of credit itself costs at most about $5,000 to $6,000 over the whole stretch, and probably less if the balance stays low.
This is a simplified model. It assumes the rates stay put, spending doesn't creep up, and the line of credit stays available. A variable-rate line can go up. I explain how a rising rate would change the plan in planning for the rate you might get.
The whiteboard version, month by month, is in a Dynamic Banking walkthrough of paying off $340,000 with a home equity line, with each month's balance written out.
Run your own version. Replace the four debts with yours, use your real rates, and see which one the first chunk should hit.