You should probably leave the account open.
If you are curious about improving your credit score (most typically defined as a FICO (Fair Isaac & Co) score, it is important to understand how your credit score is calculated. Your credit rating is calculated based on several variables, including: your payment history (do you have any late payments, charge-offs, etc.), the amount and type of debt that you owe, if you have maxed out any of your trade lines (credit utilization), and then several other secondary factors like the length of your credit history and how many recent inquiries have been made to look at your credit history.
By leaving your account open, you have an account staying listed on your credit report with a "good" payment history, it might be beneficial if it has a long account history, and lastly it will positively impact your utilization calculation since you have nothing borrowed on it.
HOWEVER, don't get lured into using it and running up debt in the future (consider putting it in a bowl of water and freezing it in the ice-box, so you cannot use it impulsively!)
These are a few of the considerations. If you would like more information, please visit our credit solutions page.
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