Depending on your credit card limit, maxing out your credit card or making a very large purchase can result in a quick drop in your credit score. This is referred to as your credit utilization ratio and it is the second most important factor in your FICO credit score.
Example: You have a credit limit of $10,000 and you carry a balance of $4,000. This means your credit utilization ratio is 40%. If your limit gets reduced to $8,000, you still have a balance of $4,000, but your ratio now stands at 50%. This has a negative influence on your credit score.