The tax implications of a joint investment account come down to two things: how the account is titled and whether the co-owners are married. Those two facts decide who reports the dividends and capital gains each year, whether putting money into the account counts as a taxable gift, and how much of the account’s built-up gain disappears when one owner dies. Get the titling wrong and you can create a nominee filing headache every April, an unfiled gift tax return, or a lost basis step-up worth tens of thousands of dollars.
How Titling Decides the Tax Answer
Brokerages generally offer three ways to title a joint account, and each one produces different answers to the same tax questions.
Joint Tenants with Right of Survivorship (JTWROS) gives every owner an equal, undivided interest. Income is split equally regardless of who funded the account. A parent who put in 100% of the money on a JTWROS account with an adult child still reports only 50% of the dividends and gains. At death, the deceased owner’s share passes automatically to the survivor outside probate.
Tenants in Common (TIC) lets co-owners hold unequal shares. Income and gains follow the ownership percentages, so a 70/30 split on the account is a 70/30 split on the 1099 income. There is no right of survivorship; the deceased owner’s share passes through their will.
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 reason to care about CP is what happens at death, covered below. Some CP states also allow Community Property with Right of Survivorship, which adds the probate avoidance of JTWROS to the basis benefits of CP.
Who Reports the Income Each Year
The brokerage issues a single 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 The IRS sees the full amount as belonging to that person. Do nothing to correct the record and the primary account holder ends up owing tax on all of it.
Nominee Reporting for Non-Spousal Co-Owners
When co-owners are not married, the primary holder is treated as a nominee for the portion of income that legally belongs to the other owner. Fixing this takes two steps. First, report the full 1099 amount on 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 separate nominee Form 1099 (the same type you received) with the IRS, along with 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 reports that nominee 1099 on their own return.
Married couples filing jointly skip this entirely, since all the income lands on one return anyway. Even spouses filing separately are not required to file nominee returns for each other.4Internal Revenue Service. General Instructions for Certain Information Returns (2025) – Section: Nominee/Middleman Returns
Skipping the nominee filing is not a free mistake. For returns due in 2026, the IRS charges $60 per form if you are up to 30 days late, $130 if you file between 31 days late and August 1, and $340 if you file after August 1 or not at all. Intentional disregard bumps the penalty to $680 per return with no maximum cap.5Internal Revenue Service. Information Return Penalties
The 3.8% Net Investment Income Tax
Higher-income owners face an additional layer. The Net Investment Income Tax is a 3.8% surtax on dividends, interest, capital gains, and similar earnings. It applies to the lesser of your net investment income or the amount by which your modified adjusted gross income exceeds the filing threshold: $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
These thresholds have not been adjusted for inflation since the tax took effect in 2013, so more taxpayers cross them every year. Each co-owner needs to check whether their share of the joint account’s income pushes them past the NIIT threshold on their individual return.
When Funding the Account Counts as a Gift
Depositing money into a joint account where someone else gains legal access can be a taxable gift. The annual gift tax exclusion for 2026 is $19,000 per recipient.7Internal Revenue Service. Frequently Asked Questions on Gift Taxes Whether the gift is “complete” — and therefore reportable — depends on the type of account.
Brokerage Accounts vs. Bank Accounts
For a JTWROS investment account, the gift happens the moment you contribute funds. A parent who deposits $50,000 into a JTWROS account with an adult child has made a $25,000 gift — the child’s 50% share.8Internal Revenue Service. Instructions for Form 709 (2025) – Section: Joint Tenancy Since $25,000 exceeds the $19,000 exclusion, the parent needs to file Form 709 to report the $6,000 taxable gift.
Filing Form 709 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 The form tracks how much of that lifetime exemption you have used.
Joint bank accounts follow a different rule. Adding someone to a bank account does not complete a gift until the non-contributing person actually withdraws money for their own benefit.8Internal Revenue Service. Instructions for Form 709 (2025) – Section: Joint Tenancy People assume brokerage and bank accounts work the same way. They do not.
Spousal Contributions
Transfers between spouses who are both U.S. citizens qualify for the unlimited marital deduction. 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 That effectively removes gift tax as a concern when married U.S. citizens fund joint investment accounts.
The unlimited deduction does not apply if the receiving spouse is not a U.S. citizen. A special 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 the $56,000 above the $194,000 limit needs to go on Form 709.
What Happens to 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 the unrealized gains that built up during the deceased owner’s lifetime, cutting the capital gains tax the survivor would otherwise owe on a sale. How much of the account gets the adjustment depends entirely on titling.
Non-Spousal JTWROS
For joint tenancy between non-spouses — say, a parent and an adult child — the default rule is that the entire account is included in the deceased owner’s estate unless the survivor can prove they contributed their own funds.12eCFR. 26 CFR 20.2040-1 – Joint Interests The executor carries that burden. Only money the survivor did not originally receive from the deceased owner counts. If the parent gave the child $100,000 and the child later put that same money into the joint account, the IRS does not credit the child with contributing.
The odd result: if the deceased owner funded 100% of the account, the entire balance is included in their estate and the entire balance steps up in basis. The survivor inherits assets at current market value, wiping out all the built-up gain. The full value also counts toward the deceased owner’s estate for estate tax purposes, though with a $15 million exemption that matters only for very large estates.9Internal Revenue Service. What’s New – Estate and Gift Tax Documentation of who contributed what is essential. Without records, the IRS defaults to including everything in the decedent’s estate.
Spousal JTWROS in a Common Law State
When spouses hold a JTWROS account and live in a common law state, exactly half the account’s value is included in the deceased spouse’s estate regardless of who contributed.13Office of the Law Revision Counsel. 26 U.S. Code 2040 – Joint Interests Only that half gets a step-up. The survivor’s half keeps its original basis.
Take a couple who bought $200,000 in stock that has grown to $600,000. The deceased spouse’s half steps up to $300,000. The surviving spouse’s half keeps its $100,000 basis. Selling the whole position the next day produces $200,000 of capital gain on the survivor’s share.
Community Property Gets the Full Step-Up
Married couples whose assets are titled as community property get the best result. When one spouse dies, both halves of the property receive a step-up in basis to date-of-death value.14Office of the Law Revision Counsel. 26 U.S. Code 1014 – Basis of Property Acquired From a Decedent Same $200,000 stock now worth $600,000: the entire position gets a new $600,000 basis. The survivor could sell everything the next day with zero capital gains tax.
On a $600,000 account with a $200,000 original basis, the common law spouse faces up to $200,000 in taxable gain on an immediate sale. The community property spouse faces none. That is the case for titling investment accounts as CP or CPWROS rather than JTWROS in the nine community property states. Couples who have moved between community property and common law states should look closely at how each account is titled, since the state where the property was acquired generally controls its character.
The Lifetime Exemption and the Paperwork Problem
The federal gift and estate tax exemption for 2026 is $15 million per person, or $30 million for a married couple.9Internal Revenue Service. What’s New – Estate and Gift Tax For most joint account holders, actually owing federal estate tax is not the real risk. The real risk is failing to file Form 709 when a contribution to a joint brokerage account crosses the $19,000 annual exclusion.
Every dollar of gift above that exclusion must be reported so the IRS can track cumulative use of the lifetime exemption. Skipping the filing saves nothing. It creates a paperwork problem that compounds over years and surfaces during estate settlement, when the people trying to resolve it are the survivors.