A request for seller concessions or credits toward assessments and taxes will depend on the details of your mortgage financing. The lower the LTV of financing, a higher percentage of seller concessions may be allowed at the closing table. This part is better addressed by your real estate attorney who will negotiate what is fair and a win/win for you and seller.
I just wanted to add that it is possible (though not at all likely) that a lender might allow you to receive up to a total of 6% of the purchase price as a concession to you at the closing. Only a few lenders allowed that sort of credit previously, and in this increasingly tight credit environment it is most likely that the lenders will not allow more than 3% of the purchase price as any type of concession or credit.
Good luck to you.
Broker Associate, Sudler Sothebys International Realty
Closing settlements on new construction and existing property are regulated by RESPA (Real Estate Settlement Procedures Act). The Settlement form is standardized and pro-rations are done to the day, typically assuming a 30 day month.
Many times on new construction, taxes have yet to be assessed by the county. The lender will usually use an estimate between 1.5-2.0% of the purchase price for the tax escrow. In my experience, this is usually a close estimate once the actual tax bill is generated. Additionally, make sure your attorney pays specific attention to the basis for the proration when your buying a new unit. For example, if the developer is paying the proration based on the prior assessment of a vacant lot, there may be a shortfall in the taxes when the actual bill is generated for a newly improved property. A good real estate attorney can help you understand proper prorations. Also, note that your real estate contract will specify the tax proration rate. For example, it is not uncommon to see taxes at a closing in Cook County prorated at 110%. Cook county taxes are paid in arrears, which means that the tax bill for a portion of time that the developer owns the property has not been levied. There could be an increase in the taxes for a portion of their ownership that is not known until after closing. The extra 10% on the pro-ration rate is there to help make up for any potential increases.
Talk with your lender or attorney about closing statements. They can get you a blank HUD so you can see how the credits/debits are tabulated at the closing.
Best of Luck.