A cash-only business owes the same federal and state taxes as any other business, and the Internal Revenue Code treats every dollar through the register as gross income regardless of how the customer paid.1Office of the Law Revision Counsel. 26 USC 61 – Gross Income Defined What changes when you run a cash-only business is the paperwork: there is no payment processor keeping a log for you, so you have to build the record yourself, send the IRS quarterly estimated payments on your own schedule, and file a separate information return any time a single customer hands you more than $10,000.
Which Taxes You Owe
The tax categories that apply to a cash business are the ordinary ones.
Income tax. Sole proprietors, partners, and S corporation shareholders report business profits on their personal returns. C corporations pay at the entity level. Most states layer their own income tax on top.
Self-employment tax. Sole proprietors and partners owe 15.3% on net earnings to fund Social Security and Medicare, split 12.4% and 2.9%.2Internal Revenue Service. Topic No. 554, Self-Employment Tax For 2026 the Social Security portion stops at the first $184,500 of combined wages and self-employment earnings.3Social Security Administration. Contribution and Benefit Base Medicare has no cap, and earnings above $200,000 pick up an additional 0.9% Medicare surtax.4Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide
Payroll tax. If you have employees, you withhold federal income tax, 6.2% Social Security, and 1.45% Medicare from their wages, and you match the 6.2% and 1.45% as the employer.4Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide Federal and state unemployment taxes apply too.5U.S. Department of Labor. Unemployment Insurance Tax Topic
Sales tax. If what you sell is taxable in your state, you collect sales tax from the customer and remit it on the state’s schedule. Taking payment in cash does not exempt the sale.
Quarterly Estimated Tax Payments
Nobody is withholding tax from your register. You have to send it to the IRS yourself, four times a year, on April 15, June 15, September 15, and January 15 of the following year.6Internal Revenue Service. Estimated Tax Estimated payments are required if you expect to owe at least $1,000 after withholding and refundable credits. To avoid an underpayment penalty, pay at least 90% of the current year’s tax or 100% of last year’s tax (110% if your adjusted gross income exceeded $150,000).7Internal Revenue Service. Penalty for Underpayment of Estimated Tax Skip a quarter and the IRS charges a penalty that works like interest on the shortfall, assessed installment by installment.
The $10,000 Cash Rule and Form 8300
Any business that receives more than $10,000 in cash from a single transaction, or from a group of related transactions, has to file Form 8300 with the IRS within 15 days of the payment.8Office of the Law Revision Counsel. 26 USC 6050I – Returns Relating to Cash Received in Trade or Business9Internal Revenue Service. Form 8300 and Reporting Cash Payments of Over $10,000 You also have to send a written notice to the person who paid you by January 31 of the following year.
Related transactions count even if no single payment reaches the threshold. If the same customer pays you $4,000 three times in a 24-hour period, the $12,000 total triggers the filing.10Internal Revenue Service. Instructions for Form 8300 Transactions spread over a longer period are also related if you know or should know they are connected.
“Cash” here is broader than currency. It includes foreign currency, certain monetary instruments with a face amount of $10,000 or less, and digital assets.8Office of the Law Revision Counsel. 26 USC 6050I – Returns Relating to Cash Received in Trade or Business
The penalty for intentionally ignoring the Form 8300 requirement is the greater of $25,000 or the amount of cash involved, up to $100,000. Failing to send the written statement to the payer carries a separate penalty of $680 per failure for 2026.11Internal Revenue Service. 20.1.7 Information Return Penalties
Records You Have to Keep
The IRS does not require a specific bookkeeping system, but whatever you use has to clearly show income and expenses.12Internal Revenue Service. Publication 583 (12/2024), Starting a Business and Keeping Records In a cash business that burden is entirely yours.
For income, keep cash register tapes, bank deposit slips, receipt books, and invoices. A workable daily routine looks like this: count the drawer at open and close, record total sales, then deposit the day’s receipts into a business bank account. The deposit slip becomes independent evidence of that day’s revenue. The IRS specifically recommends keeping business and personal accounts separate.13Internal Revenue Service. Income and Expenses 1
For expenses paid in cash, keep receipts, petty cash slips, or invoices showing the amount, the payee, the date, and the business purpose. A log kept as you go is far more credible than one assembled at tax time. If you make a lot of small cash purchases, run a petty cash fund with a written slip for each disbursement.
How Long
Keep most records for three years from the date you filed the return. The IRS can look back six years if you underreported income by more than 25% of the gross income on your return, and there is no time limit at all if you never filed or filed a fraudulent return. Employment tax records have to be kept at least four years after the tax is due or paid, whichever is later.14Internal Revenue Service. How Long Should I Keep Records?
Deducting Expenses Paid in Cash
Legitimate business expenses are deductible whether you paid in cash, by check, or by card. The problem with cash is proving them. Without a canceled check or card statement linking the payment to a vendor, your receipt is the only evidence.
Travel, meals, entertainment, and gift expenses have stricter substantiation rules. You need records of the amount, date, place, business purpose, and business relationship, made at or near the time of the expense. Documentary evidence such as a receipt is required for any expenditure of $25 or more.15eCFR. 26 CFR 1.274-5A – Substantiation Requirements For ordinary purchases like supplies or inventory, the vendor receipt showing what you bought, how much, and when is enough. A cash business that claims large deductions without receipts should expect the deduction to be disallowed on audit.
How the IRS Reconstructs Unreported Cash
The IRS does not need direct proof of cash you pocketed. It has three well-established indirect methods, documented in its own manual.16Internal Revenue Service. 9.5.9 Methods of Proof
Bank deposit analysis. An agent totals everything deposited into your accounts, subtracts known non-income items like loans or transfers between accounts, and treats the remainder as gross income. If the total exceeds what you reported, the difference is presumed unreported. This is the standard move when books are missing or incomplete.
Cash expenditure method. When the suspicion is that cash never made it to a bank, agents add up living expenses, asset purchases, and other outlays, then compare the total to reported income. Any shortfall is treated as unreported taxable income.
Percentage markup method. The agent compares your reported gross receipts to industry-standard markup percentages. A restaurant whose cost of goods implies $500,000 in sales but reports $350,000 has a $150,000 gap to explain.
In all three methods, the burden shifts to you to account for the discrepancy. The records described above are what let you do that.
Penalties if You Underreport
Filing late triggers a penalty of 5% of the unpaid tax per month or partial month, capped at 25%.17Internal Revenue Service. Failure to File Penalty Paying late adds a separate 0.5% per month, also capped at 25%.18Internal Revenue Service. Failure to Pay Penalty Interest compounds daily on top of both.
If any part of the underpayment is attributable to fraud, the civil fraud penalty is 75% of that portion, and once the IRS establishes fraud on any part the whole underpayment is presumed fraudulent unless you prove otherwise.19Office of the Law Revision Counsel. 26 USC 6663 – Imposition of Fraud Penalty
Willful tax evasion is a felony punishable by a fine of up to $100,000 ($500,000 for a corporation) and up to five years in prison.20Office of the Law Revision Counsel. 26 USC 7201 – Attempt to Evade or Defeat Tax Criminal prosecutions are not common, but the IRS has long targeted cash-heavy industries for them.