The tax implications of a joint investment account come down to two questions: how the account is titled, and whether the co-owners are married. Those two facts decide who reports the dividends and gains each year, whether putting money in triggers a gift tax filing, and how much of a basis step-up the surviving owner gets when the other dies. Get the titling wrong and you can hand the IRS tax that careful setup would have avoided.
How Titling Shapes Every Tax Answer
Brokerages generally offer three ways to title a joint account, and the choice drives everything that follows.
Joint Tenants with Right of Survivorship (JTWROS) gives each owner an equal, undivided interest. Income is split equally regardless of who funded the account, so a parent who put in 100% of the money still reports only 50% of the dividends and capital gains. When one owner dies, their share passes directly to the survivor outside probate. Either owner can withdraw or liquidate without the other’s consent, and a creditor of one owner can reach the assets.
Tenants in Common (TIC) allows unequal shares. If one person owns 70% and the other 30%, each reports income and gains in that proportion. There is no right of survivorship: a deceased owner’s share passes through their will and typically goes through probate.
Community Property (CP) is available only to married couples in nine states: Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, and Wisconsin.1Internal Revenue Service. Publication 555 (12/2024), Community Property Income is always split 50/50. The real payoff shows up at death, discussed further below. Some of these states also offer Community Property with Right of Survivorship, which pairs the CP basis treatment with probate avoidance.
Who Reports the Investment Income Each Year
The brokerage issues one Form 1099 under the Social Security Number of whichever owner is listed first on the account.2Internal Revenue Service. General Instructions for Certain Information Returns (2025) – Section: Recipient Names and Taxpayer Identification Numbers As far as the IRS is concerned, every dollar of dividends, interest, and capital gains on that form belongs to that person. If you are the primary holder and do nothing, you will be taxed on all of it.
Nominee Reporting for Non-Spousal Co-Owners
When the co-owners are not spouses, the primary holder is treated as a nominee for the other owner’s share. Fixing the record takes two steps. First, report the full 1099 amount on your Schedule B, then subtract the co-owner’s share on a line labeled “Nominee Distribution.”3Internal Revenue Service. 2025 Instructions for Schedule B (Form 1040) Second, file a nominee Form 1099 (the same type you received) with the IRS, along with a Form 1096, showing the co-owner as the recipient of their share.4Internal Revenue Service. General Instructions for Certain Information Returns (2025) – Section: Nominee/Middleman Returns The co-owner then picks up that amount on their own return.
Married couples filing jointly skip this entirely because all income lands on the same return. Spouses who file separately are also not required to file nominee returns for each other.4Internal Revenue Service. General Instructions for Certain Information Returns (2025) – Section: Nominee/Middleman Returns
Skipping a required nominee filing is not free. The IRS charges per-form penalties for information returns filed late or not at all, rising to $340 per form once you pass August 1, and $680 per form with no cap if the failure is intentional.5Internal Revenue Service. Information Return Penalties
The 3.8% Net Investment Income Tax
Higher-income owners pick up a second layer. The Net Investment Income Tax adds 3.8% to dividends, interest, capital gains, and other investment income, applied to the lesser of your net investment income or the amount by which your modified adjusted gross income exceeds the filing threshold. The thresholds are $250,000 for married filing jointly, $200,000 for single filers, and $125,000 for married filing separately.6Internal Revenue Service. Topic No. 559, Net Investment Income Tax Those thresholds have not been adjusted for inflation since the tax took effect in 2013, so more joint account holders cross them every year.
When Funding the Account Is a Taxable Gift
Depositing money into a joint account where someone else gains access to it can count as a taxable gift. The annual gift tax exclusion is $19,000 per recipient for 2026.7Internal Revenue Service. Frequently Asked Questions on Gift Taxes Whether and when the gift is “complete” turns on what kind of account you are funding.
For a brokerage account titled JTWROS, the gift happens the moment you deposit the money. A parent who puts $50,000 into a JTWROS account with an adult child has made a $25,000 gift, the child’s half.8Internal Revenue Service. Instructions for Form 709 (2025) – Section: Joint Tenancy Because $25,000 exceeds the $19,000 exclusion, the parent must file Form 709 reporting a $6,000 taxable gift. Filing the form does not mean writing a check. The excess is applied against the donor’s lifetime gift and estate tax exemption, which is $15 million per person for 2026.9Internal Revenue Service. What’s New – Estate and Gift Tax Form 709 just tracks how much of that lifetime amount you have used.
Joint bank accounts work differently: the gift is not complete until the non-contributing person actually withdraws money for their own benefit.8Internal Revenue Service. Instructions for Form 709 (2025) – Section: Joint Tenancy This catches people off guard because they assume brokerage and bank accounts follow the same rule. They do not. With an investment account, the titling itself is the transfer.
Spouses and the Marital Deduction
Transfers between spouses who are both U.S. citizens qualify for the unlimited marital deduction, so one spouse can move any amount into a joint account without gift tax consequences.10Office of the Law Revision Counsel. 26 U.S. Code 2523 – Gift to Spouse When the couple gives money from the joint account to a third party, they can elect to split the gift, applying each spouse’s $19,000 exclusion for a combined $38,000 to one recipient in 2026.7Internal Revenue Service. Frequently Asked Questions on Gift Taxes Gift splitting requires both spouses to file their own Form 709 even when no tax is owed.
If your spouse is not a U.S. citizen, the marital deduction does not apply. A separate annual exclusion caps tax-free gifts to a non-citizen spouse at $194,000 for 2026.11Internal Revenue Service. Frequently Asked Questions on Gift Taxes for Nonresidents Not Citizens of the United States A U.S. citizen who deposits $500,000 into a JTWROS account with a non-citizen spouse has made a $250,000 gift and must file Form 709 for the $56,000 above the limit.
What Happens to Cost Basis When a Co-Owner Dies
When a joint account holder dies, the cost basis of assets in the account may be adjusted up to the fair market value on the date of death. That step-up erases unrealized gains built up during the deceased owner’s lifetime, which can sharply reduce capital gains tax on a later sale. How much of the account gets the adjustment depends entirely on titling.
Non-Spousal JTWROS
For joint tenancy between non-spouses, the default rule is that the entire account value is included in the deceased owner’s taxable estate unless the survivor can prove they contributed their own funds.12eCFR. 26 CFR 20.2040-1 – Joint Interests The executor carries the burden of proof, and only money that did not originally come from the deceased owner counts. If a parent gave an adult child $100,000 and the child later deposited that same money into the joint account, the IRS does not credit the child’s contribution because the funds trace back to the parent.
The upside: if the deceased owner funded the whole account, the whole balance is included in the estate and the whole balance steps up. The survivor can sell with no built-in capital gain. The downside is that the full value counts toward the decedent’s estate, though the $15 million per-person exemption means this matters only for very large estates.9Internal Revenue Service. What’s New – Estate and Gift Tax Keep contribution records. Without them, the IRS defaults to including everything.
Spousal JTWROS in a Common Law State
When spouses hold a JTWROS account in a common law state, exactly half the account is included in the deceased spouse’s estate regardless of who funded it, and only that half steps up.13Office of the Law Revision Counsel. 26 U.S. Code 2040 – Joint Interests The survivor’s half keeps its original basis. Say the couple bought $200,000 of stock that is worth $600,000 at the first death. The deceased spouse’s half steps up to $300,000. The survivor’s half keeps a $100,000 basis. Selling the whole position the next day produces a $200,000 capital gain on the surviving spouse’s share.
Community Property Gets a Full Step-Up
Married couples with assets titled as community property get the best outcome. When one spouse dies, both halves of the property step up to the date-of-death fair market value.14Office of the Law Revision Counsel. 26 U.S. Code 1014 – Basis of Property Acquired From a Decedent Using the same stock position, the entire $600,000 balance takes a new basis of $600,000. The survivor can sell the next day with zero capital gains tax.
On a $600,000 account with a $200,000 original basis, a common law JTWROS spouse faces up to $200,000 of taxable gain on an immediate sale; a community property spouse faces none. For couples in community property states, that gap is the strongest reason to title investment accounts as CP or CPWROS rather than plain JTWROS. If you have moved between community property and common law states, review each account’s titling, because the character of the property is generally set by the state where it was acquired.
Form 709 Is Still Required Even When No Tax Is Due
The $15 million per-person exemption means that for most joint account holders, estate tax itself is not the pressing worry. The common pitfall is failing to file Form 709 when a contribution to a non-spousal JTWROS account pushes above the $19,000 annual exclusion. Every dollar above the exclusion has to be reported so the IRS can track your cumulative use of the lifetime exemption. Skipping the filing saves nothing and leaves a problem that surfaces during estate settlement, when it is hardest to fix.