Taxes on a joint bank account follow the money, not the names on the signature card. The IRS assigns interest income to whoever actually contributed the funds, treats withdrawals by a non-contributing co-owner as potential gifts, and — when one owner dies — pulls either half of the balance (for spouses) or the untraced portion (for everyone else) into the estate. Banks don’t work this way, which is where the trouble starts.
Who Owes Income Tax on the Interest
Your bank issues one Form 1099-INT per account, usually under the Social Security number of the first-listed holder.1Internal Revenue Service. About Form 1099-INT, Interest Income The IRS receives a document that looks like one person earned everything, even though two people may own the underlying cash.
Getting the 1099 doesn’t make you responsible for the full tax bill. The IRS expects each co-owner to report interest in proportion to what they put in. Deposit half the principal and you owe tax on half the interest, whatever name the bank printed on the form.
For married couples filing jointly this rarely matters, because both spouses’ income lands on the same return anyway. It matters a great deal for parent-child accounts, siblings, unmarried partners, and business associates. If you’re the primary holder on paper but someone else contributed part of the balance, you need to file a nominee return or you’ll be taxed on money that isn’t yours.
Splitting the Income With a Nominee Filing
When your 1099 includes interest or dividends belonging to a co-owner, the IRS treats you as a “nominee” for that portion.2Internal Revenue Service. Topic No. 403, Interest Received The correction has two parts.
On your own return, report the full 1099 amount on Schedule B. Below the last interest entry, write a subtotal, add a line labeled “Nominee Distribution,” and subtract the portion that belongs to the co-owner. The remainder is your taxable interest.3Internal Revenue Service. Instructions for Schedule B (Form 1040) (2025)
Then issue your co-owner their own 1099-INT (or 1099-DIV, if the income is dividends), listing you as the payer and them as the recipient for their share. File that form with the IRS along with a Form 1096 transmittal, and send a copy to the co-owner so they can pick up the income on their return.4Internal Revenue Service. General Instructions for Certain Information Returns (2025) Spouses are excused from this step: they aren’t required to file nominee returns to shift income between each other.
A concrete example. Your mother opens a savings account with $80,000 of her own money, adds you as co-owner, and you later put in $20,000. The bank sends her a 1099-INT for $2,000. She reports the full $2,000 on Schedule B, subtracts $400 as a nominee distribution (your 20% share), and issues you a 1099-INT for $400. You then report the $400 on your return.
Watch the Kiddie Tax If a Child Is the Co-Owner
Splitting income onto a minor’s return sounds like a tax break, but it often isn’t. For 2026, a child’s unearned income above $2,700 is taxed at the parent’s marginal rate rather than the child’s.5Internal Revenue Service. Topic No. 553, Tax on a Child’s Investment and Other Unearned Income The rule reaches children under 18, 18-year-olds whose earned income doesn’t cover more than half their support, and full-time students under 24 who meet that same support test. A large joint account throwing off several thousand dollars of interest for the child’s share can push you straight into kiddie-tax territory and wipe out the benefit of splitting.
When Deposits and Withdrawals Become Gifts
Putting money into a joint account is not, by itself, a taxable gift. The IRS calls it an “incomplete gift” because you can still withdraw everything you put in. A gift is completed only when the non-contributing co-owner pulls money out for their own benefit and you can’t get it back.6Internal Revenue Service. Instructions for Form 709 (2025) – Section: Joint Tenancy
Say a parent deposits $100,000 into a joint account with an adult child. Nothing has happened for gift tax purposes. If the child later withdraws $30,000 to buy a car, that $30,000 is a completed gift from the parent to the child on the day of the withdrawal.
Each completed gift is measured against the annual exclusion, which is $19,000 per recipient for 2026.7Internal Revenue Service. Instructions for Form 709 (2025) If the child’s personal withdrawals for the year stay at or below $19,000, no gift tax return is required. Above that, the parent must file Form 709 to report the excess. In the car example the parent would report an $11,000 taxable gift ($30,000 minus $19,000).
Filing Form 709 rarely means writing a check. The excess simply eats into the giver’s lifetime gift and estate tax exemption, which is $15 million for 2026.8Internal Revenue Service. What’s New — Estate and Gift Tax Actual gift tax kicks in only after that lifetime exemption is used up. Failing to file when required, though, creates a compliance problem that can resurface years later during an audit or estate settlement.
Spousal Accounts: Unlimited but Only for Citizens
Transfers between U.S. citizen spouses qualify for the unlimited marital deduction. Deposits and withdrawals between a joint spousal account carry no gift tax consequences regardless of amount, and neither spouse needs to track who contributed what.9Office of the Law Revision Counsel. 26 USC 2523 – Gift to Spouse
The unlimited deduction disappears if the recipient spouse isn’t a U.S. citizen. A special annual exclusion applies instead: $194,000 for 2026.10Internal Revenue Service. Frequently Asked Questions on Gift Taxes for Nonresidents Not Citizens of the United States If a non-citizen spouse withdraws more than that in a single year from an account funded entirely by the citizen spouse, the excess is a taxable gift and Form 709 is required. Couples who assume every spousal transfer is automatically tax-free walk into this one often.
What Happens When a Co-Owner Dies
Federal estate tax treatment of a joint account splits sharply along one line: was the co-owner a spouse or not.
Non-Spousal Accounts: The Contribution Presumption
For accounts shared with anyone other than a spouse, the IRS begins with a harsh presumption. The entire balance is included in the deceased owner’s gross estate, and the survivor can reduce that amount only by proving how much of the money they contributed.11Office of the Law Revision Counsel. 26 USC 2040 – Joint Interests Whatever portion the survivor can document as their own is excluded; the rest stays in the estate.12eCFR. 26 CFR 20.2040-1 – Joint Interests
If a father dies holding a $200,000 joint account with his daughter and she can prove she deposited $60,000 over the years, $140,000 is included in his estate and $60,000 is excluded. Without that proof, the full $200,000 is included. Keeping deposit records is not optional when the account is non-spousal.
Spousal Accounts: The Simple Half
Married couples get a much simpler rule. Exactly half of a spousal joint account is included in the deceased spouse’s gross estate, regardless of who deposited the funds, and no contribution tracing is required.11Office of the Law Revision Counsel. 26 USC 2040 – Joint Interests The surviving spouse then claims the unlimited marital deduction on the inherited half, which typically zeroes out any federal estate tax on the account.13Office of the Law Revision Counsel. 26 USC 2056 – Bequests, Etc., to Surviving Spouse
The $15 Million Exemption
The federal estate tax exemption for 2026 is $15 million per person, following the increase in the One, Big, Beautiful Bill signed into law on July 4, 2025.8Internal Revenue Service. What’s New — Estate and Gift Tax Most estates fall well below that number, so the contribution-tracing exposure on non-spousal accounts is often a state-level concern rather than a federal one. Six states impose their own inheritance taxes with much lower exemptions, and rates depend on the survivor’s relationship to the deceased, so a joint account with a sibling or adult child is worth checking against your state’s rules.
A Non-Tax Trap Worth Knowing About
Joint accounts create exposure that has nothing to do with the IRS. For Supplemental Security Income, the Social Security Administration presumes the entire balance belongs to the SSI applicant, whoever actually deposited the money.14Social Security Administration. Code of Federal Regulations 416.1208 – How Funds Held in Financial Institution Accounts Are Counted Rebutting that presumption requires statements from all co-owners, full deposit and withdrawal records, and in some cases removing your name or separating the funds. Most state Medicaid agencies apply a similar presumption for long-term care eligibility, where the individual asset limit is often just $2,000. Adding an elderly parent to your account for convenience can quietly destroy their Medicaid eligibility.
Penalties for Getting It Wrong
The IRS matches 1099s to returns. If a nominee filing was required and you skipped it, the IRS will assume the whole 1099 amount is yours and send a bill for the shortfall.
On top of the unpaid tax, the IRS can add a 20% accuracy-related penalty when the underpayment is tied to negligence or a substantial understatement of income.15Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments A substantial understatement means the correct tax exceeds what you paid by more than $5,000 or 10% of the correct tax, whichever is greater. Interest runs on both the tax and the penalty from the original due date of the return.
The fix is cheap. Nominee 1099s take a few minutes to prepare, and each co-owner reports their real share. The cost of leaving it undone compounds every year the mistake sits on the record.