The credit will probably not be equal to your total NY tax. That's why I always say that you get credit for "part or all" of the tax that you pay to New York. The credit is actually the amount of NJ tax that you would have paid on the income if it had been NJ income instead of NY income.
The following is from New Jersey Bulletin GIT-3W (page 2).
"[The] credit reduces the taxpayer’s New Jersey Income Tax; it does not necessarily entitle the taxpayer to a dollar-for-dollar credit for the total amount of taxes paid to the other jurisdiction. The credit represents the amount of New Jersey Income Tax that would have been imposed if the income earned in the other jurisdiction had been earned in New Jersey, or the amount of tax actually paid to the other jurisdiction, whichever is less."
For more details about the credit, you can download Bulletin GIT-3W from the following link.
<a rel="nofollow" target="_blank" href="
http://www.state.nj.us/treasury/taxation/pdf/pubs/tgi-ee/git3w.pdf">http://www.state.nj.us/treasury/...>
