The fundamentsl question is what did you agree about the ownership of the house when you bought it. As the house is in joint names you may have purchased it as Joint Tenants, in which case you are presumed to be entitled to equal undivided interests in the property, or you could have purchased as Tenants in Common in which case you own distinct and separate shares in the property in whatever propotions you agreed at the outset. Unfortunatelty it is all too common for joint purchasers and their conveyancers to give no thought to these matters when the purchase occurs, and the whole issue has to be worked out later on, often at great expense in the courts. In the absence of any agreement I would start on the principal that equality is equity - half each, but facts could prove otherwise. Clearly you will only get your money if he buys you out (and it is woth a dsicount to get matters sorted quickly and amicably) or if he can not buy you out the property will have to be sold. As a co-owner you have the right to demand taht the property be sold, and can obtain a court order to sell if necessary