OK - you qualify for the non FTB rate of relief so since you are outside the initial FTB 7 year period. In this case a maximum of €6K in interest qualifies for relief but according to your details it looks like you are actually paying less than €3K p.a. in interest so only that amount will qualify. Karl Jeacle's calculator suggests c. €2,661 in interest for this year given the details above which would mean €2,661 @ 20% = €532 p.a. I don't know where the €280.40 figure mentioned above comes from. Perhaps only one of you is qualifying for relief or something since this isn't too far off half the figure I came up with? Probably best to check with your lender and Revenue.