Here is the fact that surprises almost every couple who applies for a mortgage together: your loan will be priced off the lower of your two credit scores. Not the average. Not the higher one. Fannie Mae's Selling Guide instructs lenders to determine a representative score for each borrower and then "select the lowest applicable score from the group as the representative credit score for the loan" (B3-5.1-02, effective 04/22/2026). FHA works the same way. So the partner with the 780 gets the pricing of the partner with the 665, and the couple finds out about it three days before closing, in the form of a number they can't change.
That is the smallest of the surprises waiting in a co-purchase. The largest one happens at the closing table, in about thirty seconds, when the settlement agent slides a page across and asks how you want to take title. Joint tenants? Tenants in common? Most buyers have never heard the phrases before that moment, have no idea that the answer determines who inherits the property if one of them dies, and pick whichever one sounds friendlier. It is quite possibly the highest-stakes uninformed decision in American consumer finance, and it takes less time than ordering coffee.
This guide is for the people who are not married to each other, or who are but want the mechanics anyway: unmarried partners, two friends splitting a house they couldn't afford alone, siblings inheriting a plan to buy together, a parent trying to get a kid into a first home. By the end you will be able to do six specific things. Work out whose credit and whose income will actually drive your approval, and whether adding the second person helps or hurts. Choose a vesting form on purpose, with the right questions for a local attorney. Tell the difference between the deed and the loan and know which of you is exposed to what. Document unequal contributions in a way that holds up years later when nobody remembers. Hand an attorney a clause-by-clause outline of the co-ownership agreement you want, instead of paying them to interview you from scratch. And run the buyout math before you need it, including the loan-to-value wall that stops a lot of buyouts dead.
One honest caveat up front, and it runs through the whole guide: property law is state law. Vesting options, creditor protection, spousal rights, transfer taxes, and reassessment rules all change at state lines, and a few of them change at county lines. This guide tells you what the choices are and what turns on them. It cannot tell you which one is right in your state, and anyone who claims to without knowing where you're buying is guessing. Budget for one consultation with a real estate attorney licensed where the property sits. It is the cheapest insurance in the transaction.
A note before you start: this is general education about how co-purchases are underwritten and titled, not legal, tax, or personalized financial advice. Where this guide uses mortgage rates in an example, they are 6.65% for a 30-year fixed and 5.95% for a 15-year fixed — the Freddie Mac Primary Mortgage Market Survey figures for the week of 2026-08-20 — used purely as illustration. Your actual rate depends on your credit, loan-to-value, property, and lender. Every dollar figure below is either plain arithmetic shown in full or sourced inline. Run the same arithmetic against your own Loan Estimate and your own attorney's advice before you act on any of it. This site takes no lead-generation fees and no lender affiliate money, so nothing here is steering you toward a product.
Whose credit score governs — the rule and what to do about it
For a conventional loan, the lender pulls credit for each borrower and derives a representative score per person: with three bureau scores, the middle one; with two, the lower one. Then, for a loan with multiple borrowers, the lender takes the lowest of those individual representative scores and uses it as the score for the whole loan (Fannie Mae B3-5.1-02). Fannie Mae's delivery system will even reshuffle borrower positions so the lowest-scored borrower lands in the secondary position, to make sure loans with more than two borrowers get priced correctly (Loan Delivery job aid).
FHA uses the same logic through a different term. FHA calls it the Minimum Decision Credit Score, and for a loan with multiple borrowers the lender uses the lowest MDCS among borrowers who have scores. That number controls eligibility, not just pricing: below 500, no FHA financing; 500 to 579, maximum 90% loan-to-value; 580 and above, maximum financing at 96.5% LTV (HUD Handbook 4000.1).
So the practical rule is blunt. Adding a person to your loan can only hold your score constant or drag it down. It can never raise it. What a second person can raise is your income, and therefore how much house you qualify for. Those two effects point in opposite directions whenever the second person has the lower score and the needed income, which is an extremely common situation.
If you want the underlying mechanics of score bands, what moves a score, and how long negative items last, the free article what credit score do you need to buy a house covers that ground in depth. That is the informational half. The rest of this guide is the operational half: what to ask, what to sign, what to write down, and what the arithmetic looks like when you run it with your own numbers.