Co-owning a house with a sibling can make homeownership affordable that would otherwise be out of reach, but it ties your credit, your taxes, and a significant chunk of your net worth to another adult’s decisions. Before you sign anything, you need to settle four things: how you’ll hold title, how the mortgage liability actually works, what a written co-ownership agreement will require of each of you, and how the arrangement will end when one of you wants out.
How You Hold Title Changes Everything
The deed language decides who inherits the property, how creditors can reach it, and what your tax basis looks like on a future sale. Siblings generally choose between two forms.
Tenancy in Common
Tenancy in common lets each sibling own a specific percentage, and the shares don’t have to be equal. If one of you contributed 70% of the down payment, the deed can reflect a 70/30 split. Both siblings still have the right to use the whole property regardless of the percentage on the deed.
When a tenant in common dies, their share passes through their will, or through probate if there isn’t one. It does not automatically go to the surviving sibling. You could end up co-owning the house with a niece, a nephew, or a stranger your sibling named in a will you never read. Most sibling co-ownership headaches start here, because the new co-owner may have entirely different plans for the property.
Joint Tenancy With Right of Survivorship
Joint tenancy requires equal shares, and when one joint tenant dies the property passes automatically to the survivor, bypassing probate. That simplicity is the appeal. The trade-off is inflexibility: shares must be equal, and the automatic transfer overrides whatever the deceased sibling’s will says about the house.
Both forms share one useful tax feature. When a sibling dies, the surviving sibling’s basis in the deceased sibling’s share resets to fair market value at the date of death. The survivor keeps their original cost basis on their own share. On a house that has appreciated significantly, this stepped-up basis on half the property can save tens of thousands in capital gains tax on a later sale.
The Mortgage Ties You Together
Applying for a mortgage with a sibling isn’t like applying alone. The lender combines both incomes, both debt loads, and both credit histories into one underwriting decision.
Both credit scores affect the rate you get. For FHA loans, the lender uses the median score across all borrowers, so a 720 sibling paired with a 620 sibling qualifies at roughly 670. A lower combined score means a higher interest rate, which can erase the affordability advantage of splitting the payment. Debt-to-income is calculated the same way: all borrowers’ monthly debts stack against all borrowers’ combined income, so heavy student loans on one side drag down the ratio for both. Because FHA treats siblings as family, you can qualify with a down payment as low as 3.5%.
The risk most siblings underestimate is joint and several liability. Both names on the mortgage means each of you owes the full balance, not half. If your sibling stops paying their share, the lender won’t consult your private arrangement. It will pursue whichever borrower it can collect from, and every missed payment damages both credit scores equally. Your co-ownership agreement can say whatever you want about splitting costs; the lender isn’t bound by it.
Put the Co-Ownership Agreement in Writing
A co-ownership agreement is a private contract between the siblings that sets out every right and responsibility before any of them are in dispute. Without one, you’re relying on memory and goodwill to resolve situations that tend to get expensive.
At a minimum, cover these points:
- Ownership percentages and who pays what share of the mortgage, property taxes, insurance, and utilities. If contributions are unequal, explain how that maps to ownership stakes.
- A spending threshold (say, $500) above which both siblings must agree before repairs or improvements go forward, plus a rule for emergency spending.
- Who lives in the property, whether either sibling can rent out a room, how long guests can stay, and whether a non-resident sibling pays a smaller share of expenses or receives rental income.
- A right of first refusal that gives the remaining sibling the first chance to buy the departing sibling’s share, with a response deadline and a stated method for setting the price.
- A buyout valuation method chosen in advance. Common approaches include an independent appraisal, an average of two appraisals, or a comparative market analysis from a real estate agent.
- What happens if a sibling dies or becomes incapacitated. This supplements the title structure and often involves life insurance sized to fund a buyout.
Require Mediation Before Anyone Sues
Add a clause requiring both siblings to attempt mediation before either can file a lawsuit. Mediation is faster, cheaper, and far less destructive to the relationship than a partition action. Specify a timeframe for completing mediation, name a service or a method for choosing a mediator, and include a narrow exception if a statute of limitations is about to run.
Get Both Names on the Insurance Policy
Every co-owner with a financial interest in the property should appear as a named insured on the homeowners policy. If only one sibling lives in the home, the non-resident sibling still needs to be on the policy. Some insurers handle this without fuss; others may push you toward a landlord policy or require a special endorsement. Shop the coverage before assuming a standard homeowners policy covers both of you.
Taxes: Where Co-Ownership Helps and Where It Bites
Two unmarried siblings filing separate returns each get their own set of deduction limits, which can be more generous than what a married couple filing jointly receives on the same property. The reporting is more complicated, though, especially with a mortgage.
Mortgage Interest
Each unmarried co-owner can deduct mortgage interest on up to $750,000 of acquisition debt on their own return, so two siblings filing separately could deduct interest on up to $1.5 million of combined mortgage debt. The wrinkle is Form 1098: the lender issues it to only one borrower, the payer of record, showing the full interest paid on the loan.1Internal Revenue Service. Instructions for Form 1098 The sibling who doesn’t receive the 1098 can still deduct their share, but needs to document the split and may need to attach a statement explaining the arrangement.
State and Local Taxes
The SALT deduction cap, which limits the combined deduction for state income taxes, property taxes, and sales taxes, was raised from $10,000 to $40,000 starting in 2025 under the One Big Beautiful Bill Act. For 2026 the cap rises 1% to $40,400. The annual increases continue through 2029, after which the cap reverts to $10,000. Because the cap applies per return, two unmarried siblings filing as single taxpayers each get the full $40,400, for up to $80,800 in combined SALT deductions on the same property. A married couple filing jointly gets $40,400 total. This is one of the rare places where being unmarried co-owners is a genuine tax advantage.
Capital Gains When You Sell
Each sibling can exclude up to $250,000 of capital gain on sale, but only if that sibling individually meets the ownership and use test: owned and used the home as their principal residence for at least two of the five years before the sale.2Office of the Law Revision Counsel. 26 USC 121 – Exclusion of Gain From Sale of Principal Residence Two siblings who both live in the home can exclude up to $500,000 combined.3eCFR. 26 CFR 1.121-2 – Limitations
The trap: if one sibling lives in the house and the other doesn’t, only the resident qualifies for the exclusion. The non-resident sibling owes capital gains tax on their entire share of the profit. On an appreciated property, that bill can run into five figures. Talk through this scenario before you buy, because it often changes whether the arrangement makes financial sense at all.
Gift Tax on Unequal Contributions
If one sibling puts up most of the down payment but the deed gives both siblings equal ownership, the IRS may treat the difference as a taxable gift.4Internal Revenue Service. Frequently Asked Questions on Gift Taxes For 2026 each person can give up to $19,000 per recipient per year without filing a gift tax return.5Internal Revenue Service. Whats New – Estate and Gift Tax
If one sibling pays a $100,000 down payment on a house deeded 50/50, the IRS could treat $50,000 as a gift to the other sibling. That exceeds the annual exclusion and triggers a Form 709 filing. No tax is actually owed until the lifetime exemption ($15,000,000 for 2026) is exhausted, but the filing requirement catches people off guard. The cleanest fix is matching ownership percentages to financial contributions.4Internal Revenue Service. Frequently Asked Questions on Gift Taxes
Your Sibling’s Creditors Can Reach the House
Co-owning means your equity in the property is partly exposed to your sibling’s financial problems. Under tenancy in common, a creditor who gets a judgment against one sibling can put a lien on that sibling’s interest and petition for a partition sale, forcing the property onto the market so the lien can be paid from the debtor-sibling’s share. The non-debtor sibling receives their share of the proceeds but loses the house.
Joint tenancy offers one specific protection: if the debtor-sibling dies, the lien on their interest is extinguished because their ownership ended at death, and the surviving joint tenant takes the full property free of those debts. While both siblings are alive, though, a creditor can still pursue the debtor-sibling’s interest and potentially break the joint tenancy.
Bankruptcy is a related risk. The federal homestead exemption protects up to $31,575 of an individual’s equity in their primary residence, and many states set higher exemptions.6Office of the Law Revision Counsel. 11 USC 522 – Exemptions If the debtor-sibling’s equity exceeds the applicable exemption, the bankruptcy trustee may force a sale, and the non-debtor sibling again receives a share of the proceeds but loses the property.
Medicaid: A Sibling-Specific Carve-Out, but Not Full Protection
If either sibling eventually needs Medicaid-funded long-term care, the co-owned house is part of the eligibility picture. Normally, transferring a home for less than fair market value within five years of applying for Medicaid triggers a penalty period during which the applicant is ineligible. Federal law carves out an exception for siblings: a Medicaid applicant can transfer their home to a sibling with an equity interest who has lived in the home for at least one year before the applicant is institutionalized, without penalty.7Office of the Law Revision Counsel. 42 USC 1396p – Liens, Adjustments and Recoveries, and Transfers of Assets The exemption applies only to biological or adopted siblings, not step-siblings.
During the Medicaid recipient’s lifetime, the state cannot lien the home if a sibling with an equity interest lives there. After the recipient dies, though, states are required to pursue estate recovery for nursing facility and related costs. The automatic exemptions from estate recovery protect a surviving spouse and certain children; siblings are not on that list.8Medicaid.gov. Estate Recovery The state can potentially recover against the deceased sibling’s interest in the property, which may force a sale. States must offer hardship waivers, but a waiver is not a plan. If long-term care is a realistic possibility, talk to an elder law attorney about structuring ownership.
How the Arrangement Ends
Every co-ownership ends eventually. How much it costs depends on whether the siblings still agree.
Buyout or Voluntary Sale
The cleanest exit is a buyout. Follow whatever valuation method your co-ownership agreement specifies, then multiply the property value by the departing sibling’s ownership percentage to arrive at the price. If neither sibling wants to keep the property, list it and split the proceeds by ownership percentage. Recording the new deed at the county recorder’s office is inexpensive; the appraisal and any state transfer taxes are the larger line items.
Partition Actions
When siblings can’t agree on whether to sell, who buys whom out, or at what price, either co-owner can file a partition action. This is a civil lawsuit asking the court to divide the property or, more commonly for a single-family home, order it sold. Attorney fees and court costs commonly run from $5,000 to $30,000, and the case can take many months. The court orders the property sold, often at auction, and distributes the proceeds by ownership interest after the litigation costs come off the top. Court-ordered sales often fetch less than fair market value. A mandatory mediation clause in your agreement exists specifically to keep things from reaching this point.
Doing Nothing Is the Worst Option
Siblings who stop communicating about a jointly owned property create a slow disaster. Property taxes go unpaid, insurance lapses, maintenance is deferred. In most states, a co-owner who covers the full property tax bill for a sustained period can eventually claim a larger share of the equity or seek reimbursement. Meanwhile the house deteriorates and becomes harder to sell at a reasonable price. If you’ve reached an impasse with your sibling, a partition action is expensive but usually cheaper than years of neglect.