You've reached your credit limit
Your credit limit caps your spending on your credit card. Once you reach it, you're cut off. Track your spending and try capping it to below 30% of your credit limit to ensure you don't exceed it. Repeatedly going up to your credit limit could hurt your credit score.
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The exception: "If you're a person who pays in full every month, these rules don't apply as much, (but) if you're running a balance month after month, it's going to trigger a detrimental credit score," says Sherry.
To keep your credit card in play once you've reached the limit, pay down your balance or request an increase to your credit limit.
Some credit cards also have per-day spending limits. To avoid freezes to your credit card, find out your daily maximum, and keep your purchases in line.