How does NJ treats In-Plan ROTH conversion?

Question

Hello, 
I have an active 403(b) retirement account to which I am still contributing. All new contributions are ROTH.  Previously I had tax deferred (non ROTH) contribution to this account. 
Let us say, total tax deferred contribution over several years in the past is $25,000.00 and total balance of tax deferred portion is now $40,000.00 (growth of $15,000).  NJ income tax is already paid on $25,000.00 (contribution to retirement account is taxable for NJ regardless whether it is a tax-deferred account or ROTH). 
If I convert the entire balance of the tax deferred portion $40,000 to ROTH,  
a. is the growth amount of $15,000.00 taxable for NJ in the year I am converting to ROTH? 
b. or is it that for NJ, I do not need to pay tax on growth amount $15,000 for this ROTH conversion?

James L. Arrasmith · Answer

When you convert your tax-deferred portion of the 403(b) to a Roth in New Jersey, the growth of $15,000 will generally be considered taxable income for NJ in the year of conversion. This is because, while you have already paid NJ taxes on your contributions, you haven’t paid tax on the growth, and NJ treats that growth as taxable. 
 
The $25,000, which you already paid NJ tax on, will not be taxed again. However, any earnings and growth from that amount, such as the $15,000, are subject to NJ income tax at the time of conversion. 
 
Be sure to include the taxable portion in your NJ income for the year you perform the conversion, as this will affect your tax liability for that year.

Q: How does NJ treats In-Plan ROTH conversion?