Changing mortgage from single to 2 people

if 2 people bought a house before the boom and only 1 persons name was on the mortgage and now the house is roughly valued at €300k more than it was paid for, what is the tax liability for the other person to get their name on the mortgage if they are not married?

The tax liability will be on the person selling their share of the property (Capital Gains Tax). And stamp duty for person buying - if relevant.

the person who's name is on the house is not selling, they just want to put the other person on it and is not related...

If you transfer or gift part of a property to someone else, this is a disposal for Capital Gains - there may also be stamp duty implications.

You should get professional advice before you arrange the transfer.

www.taxingtimes.ie