I am considering transferring partial ownership of a property (50%) in Bolton to my partner (we are not married but have been cohabiting for several years). The property is not our main residence. 
The property is valued at £400,000. There is an outstanding mortgage (in my sole name) of £188,000. 
If she were to take a share of the property, it would be 50% value, 50% mortgage. This would equate to an equal share value of £200,000. Does it matter that we aren’t married or in an ‘official’ partnership? On what amount would she pay stamp duty land tax (SDLT)? Would this be different if it were our main residence?  

Arthur Weller replies:  

There are two issues – capital gains tax (CGT) and SDLT. If the property is worth more today than when it was originally acquired, you will have to pay CGT on half of the increase (representing half the house that you are giving away). If this was your qualifying main residence, then the capital gain would be exempt from CGT due to principal private residence relief. From what I understand, your partner is taking responsibility for a mortgage of £94,000. This is below the residential SDLT threshold, so the principal SDLT charge will not apply. See HMRC’s Stamp Duty Land Tax Manual at SDLTM00330A (Example 3). As far as the 5% SDLT surcharge is concerned, it depends on whether your partner owns any other property besides this property you are now transferring to her. If she doesn't, then it will not apply.