Legal Question in Real Estate Law in California

In a rather technical sense, you are right about the mortgage, new roof, etc. being 3/4 - 1/4, and the groceries and utilities and the like, 50-50. That's what a court would say if the property were partitioned. Also, neither of you owes rent to the other. As long as you are living together and no court jurisdiction is being invoked, the living expenses can and should be whatever you negotiate.....one on foy may have more expensive tastes than the other, perhaps.

Also, the 3/4 - 1/4 sharing is based more on necessity of the outlay than its durability. If you want a 100-year wrought iron fence at $100 a foot and she would be OK with redwood at $20 a foot, you should absorb the difference.

OK, first off, although you have probably figured this out by now, it was a boneheaded move to buy a house together without sorting this out first and putting it in writing. With that said, the fact that you are occupying the property complicates the legal situation. If it were an investment the analysis would be simple. In a partnership, when a partner pays into the partnership and it is not a loan it increases their stake in the partnership. So if you each paid half, you would be buying a larger share of the partnership. Only if the contributions match the percentage of ownership does the percentage not change. However, you are not in a pure partnership and much of the payments are for consumption, such as utilities you mention. That's a household issue, not a legal one. Unfortunately there is no bright line rule as to what will be counted as contribution to the property and what would be counted as household expenses. So better you sort that out yourselves than look for a clear legal answer. For the things that you agree contriubute to the value of the property (or if you went to court, the things the court found to be contributions to the property) you should only be paying 1/4, unless she is willing to have your share of the equity grow with your contributions. If you get years down the road and go to sell, and haven't agreed on this, you will wind up in a partition lawsuit and could well blow through more money than the amounts in dispute.