Hi.There is no allowance that you can use against rental income exclusively. You should pay tax on the rental income less deductible expenses given that your personal allowance is used against your salary. There is a list of the types of expenses you can claim here.The rule is that if your net of deductible expenses rental income is £2,500 or more per annum, you should be disclosing it in a tax return. Any profit is taxable. Take a look here for the criteria for having to complete a tax return or not having to complete one. If you need to register for self-assessment, you can do so using a form SA1 here. In my opinion, it's a good idea to complete a tax return so you can register your rental losses with the tax office for offset against profits you may make in the future.I hope this helps but let me know if you have any further questions.