Assuming your original balance was $540K in the beginning of the year and then jumped to $1M in July, your averages balance during the year is $1.54M/2= $770K. Report this in the original 1098-T and leave that box blank if you have more than one 1098-T. Some of the mortgage interest may be reduced because you are over the $750K threshold. Try this and see if this works.
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