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You are allowed to give a cash gift to any one individual a maximum of $13,000 per year without creating a taxable event. If the gift amount exceeds the $13,000 for one person, though you will not have to pay tax, you will need to file a Form 709 Gift tax Return. For 2011/2012 the lifetime gift tax exemption is $5 million dollars. To answer your question,...no you will not have to pay tax unless the downpayment is over $5 million dollars.