How credit utilization actually works

Utilization is the ratio of what you owe on revolving accounts to the total credit limit on those accounts. That definition is simple; almost every detail underneath it is not.

Which accounts count

Revolving accounts — credit cards, retail cards, lines of credit, home equity lines. Not installment loans: your car loan and your mortgage have balances, but they are not part of revolving utilization.

Charge cards with no preset spending limit are a special case. With no limit there is no denominator, so they are generally excluded — which is why a large balance on one may not move your utilization at all.

Closed accounts leave the denominator

This is the one that surprises people. A closed card’s limit no longer provides available credit, so it stops counting. Close a card with a $10,000 limit and the same balances instantly represent a higher percentage — without you having borrowed anything.

Aggregate and per-account are both measured

Your aggregate utilization is all revolving balances over all revolving limits. Your per-account utilization is each card individually. Scoring models look at both, which is why a single card near its limit can weigh on your file even when your overall figure looks reasonable.

There is a useful mathematical consequence here. With limits held constant, a dollar paid to any revolving account moves your aggregate ratio by exactly the same amount. The aggregate figure therefore tells you how much to pay; only per-account thresholds, interest rates and statement timing can tell you where.

Which balance is used

Whatever your issuer reported, which is usually the statement balance rather than your live balance. See statement closing dates versus due dates for why that distinction costs people so much.

The thresholds people cite

You will see 30% quoted constantly as a target. It is a simplification. Scoring models treat utilization as bands rather than a smooth line, and lower is generally better all the way down — the difference between 29% and 9% is usually larger than the difference between 31% and 29%.

The exact band boundaries are not published, and anyone stating them as fact is telling you more than they know. What is reliable: utilization recalculates every reporting cycle, so unlike most credit factors it can improve within a month.

Zero is not the target

Reporting zero across every card is generally read as an unused account rather than a well-managed one. A small reported balance on at least one card usually reads better than nothing at all.