Adding many new accounts at once can cause a ding to your score. Indeed, "hard" credit inquiries will affect your score for up to a year. It is best to keep new credit minimal, says Kathy Williams, a Principal and Senior Wealth Strategist at Waddell & Associates. Open those accounts that you need, and ideally don't add more than one account per year.  Most importantly, having more credit cards can be hazardous to someone who doesn't have the ability or discipline to NOT charge them to the max (behavioral side of credit), adds Williams.