The simple version

A credit limit is the most the card issuer is willing to lend you on that account at one time. It is set by the issuer, for the issuer, as a cap on its own exposure. It is not a score, not a reward, and not a statement about your worth as a customer, although it is easy to read it that way when the number comes back smaller than you expected.

How the number gets set

Issuers usually decide a limit after you apply rather than before. They review your credit report and history, along with the income information you put on the application, and set a cap they are comfortable with. A low limit can follow from a thin or troubled credit history, from balances you already carry on other cards, from low reported income, or simply from the card itself, because some products carry small limits by design regardless of who is holding them.

That last one is worth sitting with. A modest limit is sometimes a fact about the product rather than a judgment about the person, which means reading every limit as a personal verdict will sometimes be flatly wrong.

The limit can move, and it can move down

An issuer can generally raise or lower the limit on an existing account, including lowering it far enough that no available credit is left. When that happens you cannot make new charges until you pay some of the balance down. It tends to feel arbitrary and personal, and it is usually neither. It is the issuer repricing its own risk, and it can have more to do with broad conditions than with anything you did that month.

The protections most people do not know they have

Two are worth knowing before it happens rather than after. If the issuer decreases your limit, it generally cannot charge you over-limit fees or a penalty rate for exceeding the new lower limit until 45 days after it has given you notice. And in most instances the issuer must give you an adverse action notice when it lowers a limit or closes an account, a notice that must either state the specific reasons or let you request them.

The second one is the useful one. A cut limit usually arrives feeling like a decision handed down without explanation. There is a mechanism for getting the explanation, and asking for it costs nothing.

Why a cut stings twice

Your limit is the bottom half of the ratio between what you owe and what you could borrow. Pay down nothing, have the limit cut, and that ratio gets worse on its own, which can move your credit score without a single change in how you behaved. This is the part that catches people. From your side the account looks identical, and the scoring does not agree. How much that ratio is weighed is a subject of its own, and the credit scores lesson handles it.

The Real Cost lens

The real cost of misreading a limit is behavioral, and it runs in both directions. Treating a high limit as money you have produces balances the limit was never permission for. Treating a low one as a verdict pushes people to open more accounts chasing a bigger number, which is its own expense. The limit is a ceiling on the bank's risk. It is not a budget and it is not a grade, and the useful question is never how much could I borrow. It is how much can I repay in full this month.

What this means

Read a limit as a business decision rather than a verdict, keep your usage well underneath it so that a cut cannot do much damage on its own, and if one does get cut, ask for the specific reasons instead of guessing at them. If the reason traces back to something in your credit report, you are entitled to a free report from each of the major consumer reporting companies every 12 months, and reading it is the cheapest way to find out whether the reason is even accurate.

What this is NOT

This is not advice about your situation, and not a recommendation for or against any card, issuer, or product. This is not a claim about what any particular issuer will do, or why it did what it did. This is not legal advice about your rights under any consumer credit law, and the protections described here are general rules carrying conditions and exceptions that your own card agreement and disclosures govern. This is not a buy, sell, or hold signal on any security. This is not financial advice.

Sources

• Consumer Financial Protection Bureau, Why did I get a low credit limit on a credit card? (that issuers set the limit after you apply by reviewing your credit report, history, and the income you reported, the common reasons behind a low limit, and the adverse action notice): https://www.consumerfinance.gov/ask-cfpb/why-did-i-get-a-low-credit-limit-on-a-credit-card-en-11/
• Consumer Financial Protection Bureau, Can my credit card issuer reduce my credit limit? (that issuers can raise or lower limits including to no available credit, the 45 day protection from over-limit fees and penalty rates after a decrease, and the adverse action notice requirement): https://www.consumerfinance.gov/ask-cfpb/can-my-credit-card-issuer-reduce-my-credit-limit-en-74/
• No market figure is asserted in this article. The two durations named are fixed consumer-protection timeframes, not rates or prices, and the terms of your own account are in your card agreement.