Unlike child support, there is no formula to work from when determining alimony.  You can find the NJ statutory criteria here.  Some of the factors would include the length of the marriage, income of each of the spouses, lifestyle and other needs.  Not every divorce will have alimony involved.  There has to be a need for support and it has to be requested.

And, if spousal support is provided, it might not be paid forever.  There are a few kinds of support:

Mediation allows the spouses to agree on the form of support that best fits your situation.  Post-divorce budgets are helpful in determining how each party can live on what they earn or receive.  The danger in litigating a divorce is that a judge will arbitrarily set the amount of alimony.  If you asked 10 different experts, you would most likely get 10 different answers since every judge and lawyer (or human being) come with built-in biases and perceptions.