The first 12 months after vacating it as your PPR are exempt from CGT. Thereafter CGT applies. If, for example, you vacated it now and rented it for 5 years before selling (i.e. owned for 15 years, PPR for 10, rented for 5) then you would be liable for CGT at 20% on (5-1)/15 = 4/15ths or 27% of any capital gain arising. Just dealing in round years for simplicitly here. The normal CGT calculations apply (e.g. indexation of the purchase price up to c. 2003, deduction of allowable expenses from the gross gain allowed etc.). Mortgage issues are irrelevant to the CGT issue although they may be relevant to the rental income taxation issue - e.g. any mortgage outstanding that was used to purchase the erstwhile PPR/now rented property can be offset against rental income when calculating tax liabilities. You should get professional advice on all of the tax and other implications of renting out your PPR.