Short answer no, you can't offset rental expense against rental income. you can however offset 75% of interest expense on the mortgage of the property you are renting (subject to registering with PTRB), depreciation on furniture, letting agent fees, accountant fees etc. There are a number of expenses you can offset. Then tax and PRSI are payable on the profit. Also you may have a rate change on your mortgage to reflect that it is no longer a PPR and are no longer eligible for interest relief. Also consider that if you have a tracker mortgage the 75% interest deduction may not be significant. And the additional income will be counted for other things, eg further education grants, eligibility for welfare payments. So it is worthwhile doing the numbers as there may be a significant cost to moving overall. But for a lot of people it is not just a money issue, it is a suitable accomodation or proximity to where the work is issue. And of course there are plenty of people who do not declare the income.