I am looking at moving and keeping my existing property. The new mortgage will be around 650K and the existing mortgage is 300k. The house was bought 6 years ago. My understanding is that I get mortgage interest relief for another year on the rented property and for 7 years on the new one. I will get around 1200 rent. My understanding is that I will have to pay around 200 in tax on this (1200-800(interest amount)X.42). But will get around 100 in interest relief on the rented property. Does this sound right?