Every debt calculator asks a question you can't answer yet
Open any debt payoff tool and it asks how much extra you can put toward debt each month. Most people guess. The guess is usually wrong, and it’s usually too high, which means the plan breaks in month three and takes their confidence with it.
Your margin is the gap between what comes in and what actually goes out. Not what you meant to spend. What left the account.
Find it in one sitting
Pull the last ninety days from every account. Not one month, because one month lies to you: it either misses the car registration and the birthdays, or it happens to contain all of them.
Total the income. Total the spending. Divide the difference by three.
That’s your real margin. It is almost always lower than the number people guess, and it is the only number worth putting in a calculator.
When the number is zero
Sometimes the honest answer is that there’s nothing left, or less than nothing. That’s worth knowing on day one rather than month four. It also means the debt ordering question is beside the point for now, because with no margin at all the snowball and the avalanche produce identical results. There’s nothing extra to aim anywhere.
The work at that stage isn’t picking a payoff method. It’s finding the first hundred dollars.