Updated August 6, 2026. Quick answer: the words on the deed decide what happens if one of you dies, and for an unmarried couple they decide it completely, because no marital right steps in behind them. Joint tenancy with right of survivorship passes the house to the survivor automatically. Tenancy in common passes the deceased owner’s share to their family. Both are one line of the same document.
The line on the deed that decides it
Cornell’s Legal Information Institute puts the difference plainly. Joint tenancy “creates a right of survivorship, which means that when one owner dies, the other owners absorb the deceased owner’s interest.” Tenancy in common does the opposite: “A TIC typically has no right of survivorship. This means that if A and B are tenants in common of Blackacre, and A dies, A’s share does not go to B.” It goes wherever A’s will sends it — or, if there is no will, wherever the intestacy statute sends it, which is to A’s relatives.
That is the scenario worth picturing before closing, because it is not rare and it is not theoretical: the surviving partner owns half a house with the deceased partner’s parents or children, who can ask a court to force a sale. A married couple in the same position usually has a third option, tenancy by the entirety, which the LII notes is “recognized in most states, available only to married couples” and which also shields the home from one spouse’s creditors. It is not available to you.
So: if the goal is that the survivor keeps the house, say joint tenants with right of survivorship on the deed and check that the recorded document actually says it. Survivorship language is a formality that states construe strictly, and a deed that merely names two people usually creates a tenancy in common by default.
When you are not putting in the same money
Survivorship and fair shares are different questions, and joint tenancy answers only the first. If one of you brings the down payment and the other pays the mortgage, joint tenancy still splits the house in half. Tenancy in common lets you own it in the proportions you actually paid — and then you need a written co-ownership agreement covering who pays what, what happens if one of you wants out, how a buyout is priced, and who has the first right to buy. Without that agreement the fallback is a partition action, which is a lawsuit that ends in a sale.
You can also have both: tenancy in common in unequal shares, with each of you leaving your share to the other by will or by a transfer-on-death deed. TOD deeds are indifferent to marital status — California’s statute, for instance, conditions eligibility on the type of property and the execution formalities and contains no marital-status condition at all — and they are a different instrument from joint tenancy, revocable in a way that joint tenancy is not.
Adding a partner to a deed you already own is a gift
This one surprises people. If you own the house and put your partner on the title without their paying for it, the Treasury regulation treats it as a gift: “If A with his own funds purchases property and has the title conveyed to himself and B as joint owners, with rights of survivorship… there is a gift to B in the amount of half the value of the property.” A married couple would be covered by the unlimited marital deduction; IRC §2523(a) grants it only where the donee “at the time of the gift is the donor’s spouse”, so it does not reach you.
The practical consequence is usually a filing, not a bill. The annual exclusion is $19,000 per recipient for 2026; half a house is normally far above it, so a Form 709 is generally required for the year, with the excess applied against your lifetime exclusion. Most couples owe nothing and simply have to file. Doing it without knowing is the problem, not the tax.
What the survivor’s tax basis becomes
Here the unmarried rule is genuinely different, and it is more often a benefit than a penalty. IRC §2040(a) includes in the deceased joint tenant’s estate the whole value of the property except the part “shown to have originally belonged to such other person and never to have been received or acquired by the latter from the decedent for less than an adequate and full consideration in money or money’s worth.” Spouses get a flat half under §2040(b) no matter who paid.
Because basis follows what the estate had to include, a surviving partner who cannot document their own contribution typically gets more of the house stepped up to its date-of-death value, not less — which lowers the tax if they sell. The inclusion only costs anything at estates far above the federal exclusion. Keep the contribution records anyway: the rule is written as a burden of proof on the survivor, and which side of it helps you depends on facts you cannot know in advance.
On a later sale, each of you has your own $250,000 exclusion under IRC §121, not the $500,000 a married couple filing jointly can reach, and each must independently have owned and used the home “for periods aggregating 2 years or more” in the five years before the sale. Those figures are fixed in the statute rather than indexed.
Sources
Cornell Legal Information Institute Wex entries for joint tenancy, tenancy in common and tenancy by the entirety; 26 C.F.R. §25.2511-1, IRC §§2511, 2523, 2040 and 121 at the LII; the annual exclusion from the IRS Frequently Asked Questions on Gift Taxes and Rev. Proc. 2025-32; Cal. Prob. Code §5642 at California Legislative Information. All read 2026-08-06.
Honest gap: we could not verify that any state extends tenancy by the entirety by that name to registered domestic partners or civil union partners, so this page does not claim it either way. If you are registered in a state that recognises the status, it is worth asking specifically.
See methodology and corrections. General information about published statutes, not legal advice. No affiliate links, nothing sold.