Under the new tax law, mortgage interest on oneu2019s personal residence and on a second home is deductible, but with limitations.Where previously a married couple filing jointly could deduct interest on up to $1 million of u201cacquisition indebtedness,u201d they can now deduct interest on $750,000. They could also deduct interest on up to $100,000 of an equity loan, such as a HELOC, but that provision no longer existsu2014that interest is no longer deductible.I have used numbers for a married couple filing jointly. For single taxpayers or married people filing separately, the deductibility of acquisition indebtedness for has been reduced to $375,000 from $500,000. People who bought their homes prior to 12/31/17 will still be able to claim interest on acquisition indebtedness up to $1 million ($500,000 single taxpayer).A homeowner will be able to refinance a loan placed before 12/31/17 and still deduct interest on up to $1 million ($500,000 single) provided that they do not increase the loan amount over the acquisition indebtedness. In other words, if the loan balance is $950,000 today and they refinance to $1 million, they will only be able to deduct interest on $950,000. Furthermore, if they happen to pay the loan down, then refinance up to the original acquisition indebtedness amount, they will only be able to deduct interest on the amount refinanced. They may be able to deduct more if the cash proceeds are used to u201csubstantially improveu201d the property. In any case, they will not be able to deduct interest on any amount above the acquisition indebtedness.I hope this is helpful.Joeu2019s standard disclaimer: While I do my best to write accurate, factual answers on tax matters, the reader should be aware that I am not a CPA or tax lawyer. You should consult a licensed tax professional for tax advice. This is only an academic discussion, even though there may be some specific examples.