If you are using conventional financing the seller can only pay 3% of all closing cost and pre-paid items.
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Speak with your agent, your attorney and your mortgage broker. Your mortgage broker should be best able to answer this for you, as he or she will have an estimate of what your closing costs will be. What is allowed to be paid by the seller towards your closing costs will depend on your particular loan program - some loan programs will only accept a seller credit for non-recurring closing costs (inspections, appraisal, etc.) while other loan programs may also allow the credit to cover pre-paids, such as pre-paid mortgage interest, homeowners insurance, etc.
Speak to the professionals you are working with to identify the specifics of your purchase.