A random ACH deposit is almost always one of three things: a legitimate payment you weren’t expecting (a tax refund, benefit, reimbursement, or promotional bonus), a processing error that routed someone else’s money to your account, or the opening move in a money-mule scam. ACH stands for Automated Clearing House, the nationwide network that moves electronic payments between banks in batches.1Nacha. Nacha Operating Rules – New Rules Before you spend a dollar of it, figure out which category yours falls into.
Read the Line on Your Statement First
The transaction description carries most of the clues. ACH entries are tagged with a short code that tells you what kind of payment it is:
- PPD (Prearranged Payment and Deposit) covers direct-deposit paychecks, government benefits, and recurring personal payments.
- CCD (Corporate Credit or Debit) is used for business-to-business payments like vendor invoices.
- WEB (Internet-Initiated Entry) is used for person-to-person transfers and payments authorized online.
These codes sit next to the sender’s name, or an abbreviated version of it.2Payments Innovation Alliance. ACH File Details Your bank may add its own label like “ACH DEP” or “DIRECT DEP.” Read the whole line carefully. A partial company name or an unfamiliar abbreviation is often all you need to jog your memory.
The Usual Sources of a Surprise Deposit
The IRS
Tax refunds, stimulus payments, and certain tax credits arrive by ACH with “IRS TREAS 310” in the company name field and “TAX REF” in the description. If the number reads “449” instead of “310,” part of your refund was redirected to cover a delinquent debt such as unpaid student loans or back child support.3Bureau of the Fiscal Service, U.S. Department of the Treasury. Tax Refund Frequently Asked Questions Federal benefit payments, including refunds, use the PPD format code.4TFX – Treasury. A Guide to Federal Government ACH Payments If you’re not sure whether the refund is really yours, check the “Where’s My Refund?” tool or call the IRS at 800-829-1040.
Social Security
Retirement, disability, and survivor benefits are paid by direct deposit, as federal law requires.5Social Security Administration. Direct Deposit The date they hit follows a fixed monthly schedule based on birth date: the second Wednesday of the month for birth dates on the 1st through 10th, the third Wednesday for the 11th through 20th, and the fourth Wednesday for the 21st through 31st.6Social Security Administration. Schedule of Social Security Benefit Payments 2025 If your deposit lines up with one of those Wednesdays, that’s a strong hint.
Employers and Insurers
An unexpected payroll credit might be a retroactive raise, a late-arriving expense reimbursement, a bonus, or a final paycheck from a former employer. Look for the company name or the payroll provider in the description.
Insurance companies pay claims and annuities the same way. A property damage settlement, a health insurance reimbursement, or a life insurance benefit can land without much notice. The company identifier isn’t always obvious, so calling your insurer to confirm the source is often faster than guessing.
Your Own Bank
Banks credit your account for their own reasons too: interest earned, a promotional bonus for opening an account, or a refund of a fee they charged in error. Account-opening bonuses often depend on conditions you may have met weeks ago, like maintaining a minimum balance or setting up direct deposit. These entries usually carry the bank’s name or a tag like “PROMO.”
When It’s a Processing Error
The ACH system matches transactions by account number, not by the name on the account. A single wrong digit typed by a payroll clerk or a bookkeeper can drop somebody else’s paycheck into your account. Errors like this happen most often during manual data entry, when a company sets up a new payee or switches banks.
Software glitches cause duplicates. If a bank uploads the same payment file twice, you may see the same credit two days in a row. System migrations and updates occasionally repost old transactions as new ones. In every one of these cases, the money shows in your balance but does not belong to you.
When It’s a Scam
Criminals use the ACH network to route stolen funds through the accounts of people who don’t know they’re being used. The FBI calls this a money mule scheme, and it usually opens with a fake job offer, an online romance, or an unsolicited payment followed by instructions to move the money somewhere else.7FBI. Money Mules
Watch for these patterns:
- A “work from home” job that asks you to receive ACH deposits and forward the money by wire, keeping a percentage as your pay.
- Someone you met online, on a dating site or social platform, asking you to accept money into your account and send it on.
- An overpayment scenario, where someone sends more than expected and asks you to return the difference by wire, gift card, or cryptocurrency. The original deposit then gets reversed, and you’re on the hook for whatever you sent back.
A legitimate employer will never ask you to process payments through your personal bank account.7FBI. Money Mules If anyone contacts you about an unexpected deposit and asks you to move the money, don’t. Report it to your bank and file a complaint with the FBI’s Internet Crime Complaint Center at ic3.gov.
How to Identify the Sender
Start with your own records. Recent tax filings, insurance claims, employer emails, class action notices, and any direct-deposit setups you’ve done. Many “mystery” deposits are things you initiated and forgot.
If nothing rings a bell, call your bank and ask for two specific pieces of information:
- The ACH trace number, a 15-digit identifier that tracks the payment from the sending bank to yours.2Payments Innovation Alliance. ACH File Details
- The company identification number, a 10-digit code in the batch header that identifies the originator.
Together those numbers tell your bank exactly who sent the money and when. While you’re waiting for an answer, leave the money alone. Move it out of your everyday spending balance if you have to, but don’t spend it.
What Happens If You Spend Money That Isn’t Yours
The Sender Can Sue You
Under the doctrine of unjust enrichment, receiving money by mistake doesn’t give you the right to keep it. The original sender retains the right to recover it, and if you spend the funds and refuse to return them, they can sue you in civil court for the amount, plus interest and legal costs depending on the circumstances.
You Could Face Criminal Charges
Most states criminalize keeping property you know was delivered by mistake if you make no effort to return it. The charge may be labeled theft, larceny, or conversion depending on the jurisdiction, and the severity generally scales with the amount, with larger sums crossing into felony territory.
The IRS Wants Erroneous Refunds Back
If the deposit is a mistaken IRS refund and you don’t return it, the IRS can treat the amount as taxable income for the year you received it.8Internal Revenue Service. 21.4.5 Erroneous Refunds To send it back, ask your bank’s ACH department to return the funds to the IRS, then call the IRS at 800-829-1040 to explain. Interest can accrue on an erroneous refund until it’s repaid.9Internal Revenue Service. Topic No. 161 – Returning an Erroneous Refund
Reversals Can Overdraw You
When a bank reverses an erroneous credit, it debits the full amount from your account. If you already spent the money, the reversal can push your balance negative and trigger overdraft fees. Banks may also freeze the account entirely if their fraud systems flag the deposit as suspicious, and while that freeze is in place you may lose access to funds that legitimately belong to you.
How Reversals Actually Happen
On the sender’s side, NACHA rules give the originating bank five banking days after the settlement date to transmit a reversal through the network.10Nacha. ACH Network Rules – Reversals and Enforcement After that window closes, the sender generally has to contact you or your bank directly and request a voluntary return. That five-day clock is why speed matters. Report the deposit right away and the reversal can usually go through normal channels without any further mess.
Federal agencies work on a longer timeline. Social Security, for instance, can reclaim benefit payments issued after a recipient’s death, with 120 days from learning of the death to send a reclamation notice to the bank and up to three years after that for Treasury to actually debit the funds.11Social Security Administration. Overview of the Reclamation Process for Title II and Title XVI Electronic Funds Transfer Payments Banks that receive a reclamation notice must return whatever is still in the account.
Once you’ve identified the source and either returned the money or confirmed it’s yours to keep, the situation is resolved. If it turns out to be a scam attempt, keep your report to the bank and to ic3.gov on file in case the reversal creates problems later.