I have a Mortgage that I make monthly payments on. In December 2018, I made a payment toward that mortgage part way through the month (let's say December 15th for simplicity). The interest is compounded daily. Is the interest that accrues from the 16th until the end of the month tax deductible for 2018 even though I won't actually be paying that interest until 2019?
In short, is the interest calculation required for Federal USA taxes based on payments in 2018 or based on interest accrued in 2018?