Capital Gains Tax and PhD Stipend

I have a tax-free PhD stipend which is greater than the personal allowance and I get about £900 a month from rent in a property where I am not resident. I have no other forms of income. How much capital gains tax do I have to pay? If the stipend was not tax-free I would pay according to basic rate taxpayer rules, but it is tax-free so what rules do I follow to figure out how much I owe?

Hi,
Capital gains tax is charged where an asset is disposed of for more that it was acquired for.  
Income from property is chargeable to income tax.
 A self assessment tax return is required to declare your rental property income.  
You can check to register for self assessment at:
Check how to register for Self Assessment if you are not already registered.
Thank you