How do I know if I contributed too much to my traditional IRA?  

You can contribute no more than $7,000 ($8,000 if you're 50 or over) to all of your traditional and Roth IRAs. Any more than that is considered an excess contribution and will be taxed at 6% per year. 

How do I avoid the 6% tax on excess contributions? 

To steer clear of the 6% tax, file a withdrawal request. Contact your financial institution and request to withdraw the excess contribution, plus earnings, by the due date of the return (including extensions).

The earnings are included as taxable income for the year the excess contribution was made.