Information on Mortgage Interest Relief (officially, Mortgage Interest Tax Relief at Source) is at http://www.revenue.ie/trs/mortgage/. I found out about the scheme just a couple of months ago when it became necessary for me to learn more about the tax system after being made redundant.
I found the page by searching for â€˜mortgage interestâ€™ on http://www.revenue.ie.
For future relief, I applied online at https://www.revenue.ie/trs/details.jsp. Future relief will reduce whatâ€™s paid rather than show up as money being returned.
For previous years, the FAQ at http://www.revenue.ie/faqs/trs_relief.htm#12 has a link to a form at http://www.revenue.ie/forms/trsp.pdf. You need to fill out the form and send it and copies of your mortgage interest statements to the address shown on the form. Past relief gets credited to your bank account. Getting back lump sums for 20% of the mortgage interest paid over nearly the last five years came in very handy right now.
You can only claim for the previous four years, so if you bought your house in 2002, youâ€™d better act quickly.