ADP Tax Codes: Federal, State, and Local Explained

ADP tax codes are internal reference keys that connect each employee’s profile to the correct withholding calculations at the federal, state, and local levels. They are not rates or dollar amounts. Each code tells the payroll engine which calculation to run, which wage base and limit to apply, and which taxing authority receives the money. For 2026, the codes have to work against a Social Security wage base of $184,500 and a federal supplemental wage rate of 22%, plus whatever your state and city require.¹

What a Tax Code Actually Points To

Think of each code as a pointer. It links an employee’s W-4 elections, work state, home address, and benefit choices to the rate tables and wage limits stored in ADP. When something changes on the profile, the code triggers a recalculation. A federal income tax code points to the progressive bracket tables. A Social Security code applies 6.2% until year-to-date wages reach the cap, then stops. A local code layers a city or county tax on top of everything else. The layering is where complexity lives, and it’s where most payroll errors start.

Federal Tax Codes

Federal codes generally carry a “FED” prefix and cover the taxes every U.S. employer withholds and remits.

Federal Income Tax (FIT)

The FIT code connects an employee’s W-4 information to the IRS’s bracket tables. Filing status, dependent credits, and any extra withholding the employee requests all feed the calculation.² If an employee never turns in a W-4, the IRS requires the employer to withhold as though the worker is single with no entries on Steps 2 through 4 — the maximum default.³

FICA: Social Security and Medicare

FICA codes cover the two taxes that fund Social Security and Medicare. Both the employee and employer pay matching amounts, so the codes track the employee’s share and the employer’s obligation separately.

Social Security (OASDI): 6.2% on wages up to the 2026 wage base of $184,500. Once year-to-date earnings hit the cap, the code stops withholding for the rest of the year.¹
Medicare (HI): 1.45% on all wages, no cap.⁴
Additional Medicare Tax: an extra 0.9% on wages above $200,000 in a calendar year. The employer starts withholding once the employee crosses the threshold, regardless of filing status, and does not match the additional amount.⁵

Federal Unemployment Tax (FUTA)

FUTA is employer-only, so employees never see it on a paystub, but it still runs through ADP’s code structure. The gross rate is 6.0% on the first $7,000 of each employee’s wages per year. Employers in states with paid-off federal unemployment loan balances get a credit of up to 5.4%, bringing the effective rate to 0.6%. States with outstanding balances lose part of that credit, and the effective rate rises for employers there.⁶⁷

State and Local Tax Codes

State codes usually use the two-letter state abbreviation as a prefix and cover three main categories: state income tax (SIT), state unemployment insurance (SUI), and, where applicable, state disability insurance (SDI) or paid family leave contributions. Each state sets its own rates, brackets, and taxable wage bases, so the codes vary widely. State unemployment wage bases alone run from $7,000 in some states to over $60,000 in others.

Local codes add the final layer. Cities, counties, and school districts in certain states impose their own income or occupational taxes. These are the most numerous and variable codes in the system. An employee who works in one city and lives in another may need two local codes, one for the work location and one for the residence, depending on whether the jurisdictions offer credit for taxes paid to the other.

Multi-State Employees and Reciprocity

When an employee lives in one state and works in another, the employer generally withholds for the work state. Many neighboring states have reciprocal agreements that let the employee pay tax only to the home state. If a reciprocal agreement applies, the ADP administrator sets up the profile to withhold only for the residence state. Without reciprocity, the employee may need withholding in both states and will claim a credit on a personal return to avoid double taxation.

Remote work has made this messier. An employee who occasionally works from home in a different state than the employer’s office may trigger withholding obligations in both places. ADP’s codes can handle multi-state setups, but the administrator has to know which states are involved and whether any reciprocal agreements or convenience-of-the-employer rules apply.

How Pre-Tax Deductions Change the Taxable Base

Not every dollar of gross pay is subject to every tax. Section 125 cafeteria plan deductions, including health insurance premiums, flexible spending accounts, and dependent care contributions, reduce taxable wages before FICA and federal income tax run. The IRS treats salary reduction contributions under these plans as amounts the employee never received, so they escape federal income tax, Social Security, and Medicare entirely.⁸

ADP handles this through deduction codes that interact with the tax codes. A pre-tax health insurance deduction code tells the system to subtract the premium from gross wages before running the FIT and FICA calculations. A post-tax code, like a Roth 401(k) contribution, reduces take-home pay but doesn’t lower the taxable base. Getting a deduction code’s tax treatment wrong means either over-withholding, which the employee will notice immediately, or under-withholding, which the IRS will notice eventually.

Supplemental Wage Codes

Bonuses, commissions, and other supplemental payments get their own withholding treatment. For 2026, the federal flat rate for supplemental wages is 22%. If an employee’s total supplemental wages exceed $1 million in a calendar year, the rate on the excess jumps to 37%.¹

ADP handles supplemental wages by applying either the flat rate or the aggregate method, depending on how the payroll run is structured. The aggregate method combines the supplemental payment with the employee’s regular pay for that period and calculates withholding on the total as though it were a single paycheck, which often produces higher withholding. The flat-rate method is simpler and usually more predictable for the employee. State supplemental rates vary and are tracked by separate state-level codes.

Setting Up Codes for a New Employee

Setup starts with three pieces of information: the completed W-4, the employee’s home address, and the physical work location. The W-4 gives you federal filing status and any withholding adjustments. The addresses determine which state and local codes apply. Most states also require their own withholding certificate, and it may allow different elections than the federal W-4.

The ADP administrator enters the filing status, dependent credits, and any additional withholding amount into the employee’s profile. The system maps that data to the correct FIT calculation. State and local codes are assigned based on work and home jurisdictions. If the employee has pre-tax benefit deductions, those codes are linked so the system reduces taxable wages before calculating withholding.

The assignment isn’t a one-time event. Codes need review whenever an employee submits a new W-4, changes a home address, transfers to a different work location, or enrolls in a new benefit plan. Failing to update promptly is the single most common source of payroll tax errors.

Common Code Errors and How to Fix Them

The most frequent problem is a stale address. An employee moves across a state line or into a new city’s tax jurisdiction and nobody updates the profile. The old state and local codes keep running, money goes to the wrong taxing authority, and the new jurisdiction gets nothing. By the time someone catches it, usually at W-2 season, the employer has to file corrections, potentially pay late penalties to the correct jurisdiction, and help the employee sort out returns in two states.

A close second is a badly completed or outdated W-4. If withholding is set to married filing jointly when the employee should be single, federal income tax will be under-withheld all year. The employer should review W-4 elections when they notice a significant discrepancy, but the accuracy of the certificate itself is the employee’s responsibility.

Correcting past errors runs through ADP’s adjustment features. If taxes were over-withheld, the employer refunds the excess to the employee and reduces the next deposit to the taxing authority by the same amount. If taxes were under-withheld, the employer must collect the shortfall from the employee and remit the corrected amount. FICA errors caught in the same calendar year are straightforward. Errors that cross calendar years often require an amended return on Form 941-X and may limit the employer’s ability to recover funds from future paychecks.

When the wrong state code was used entirely, meaning withholding went to State A but should have gone to State B, the employer typically has to file for a refund from the incorrect state and remit to the correct one. These cross-state corrections are slow and paper-heavy, which is why getting the initial setup right matters more than most administrators realize.

How the Codes Drive Reporting and Deposits

Every tax code feeds into compliance reports. The codes allocate withheld funds to the correct federal, state, and local ledgers, and those ledgers generate the forms the government expects to see.

Quarterly, FIT and FICA code data populates Form 941, which reports total wages paid, federal income tax withheld, and both the employee and employer shares of Social Security and Medicare tax. Form 941 is due the last day of the month after each quarter: April 30, July 31, October 31, and January 31.⁹ Annually, the same code-driven data produces Form W-2 for each employee, showing total wages and every category of tax withheld. Employers furnish copies to employees and file with the Social Security Administration.¹⁰ FUTA codes feed Form 940. Discrepancies between what the codes withheld and what these forms report are exactly what triggers IRS notices.

Deposit timing runs on a separate schedule the IRS assigns based on a lookback period. If total tax liability during the lookback was $50,000 or less, deposits are monthly, due by the 15th of the following month. Above $50,000 puts the employer on a semi-weekly schedule. A single day’s accumulated liability of $100,000 or more triggers a next-business-day deposit and moves the employer to semi-weekly for the rest of that year and the next.¹¹¹ Late deposits carry penalties that escalate from 2% to 15% depending on lateness and IRS notice status, and withheld income tax and the employee’s share of FICA are trust fund taxes, meaning responsible individuals can be held personally liable for 100% of the unpaid trust fund amount.¹²¹³

The codes do the arithmetic, but they only calculate against the profile data you give them. Keep the W-4, the addresses, and the benefit elections current, and the rest of the system does what it was built to do.

1
Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide
2
Internal Revenue Service. About Form W-4, Employee’s Withholding Certificate
3
Internal Revenue Service. Form W-4 – Employee’s Withholding Certificate
4
Social Security Administration. Contribution and Benefit Base
5
Internal Revenue Service. Topic no. 560, Additional Medicare Tax
6
Internal Revenue Service. Topic no. 759, Form 940, Employers Annual Federal Unemployment Tax Act (FUTA) Tax Return
7
U.S. Department of Labor. FUTA Credit Reductions
8
Internal Revenue Service. FAQs for Government Entities Regarding Cafeteria Plans
9
Internal Revenue Service. Topic no. 758, Form 941, Employers Quarterly Federal Tax Return
10
Internal Revenue Service. Topic no. 752, Filing Forms W-2 and W-3
11
Internal Revenue Service. Notice 931
12
Internal Revenue Service. Failure to Deposit Penalty
13
Office of the Law Revision Counsel. 26 USC 6672 – Failure to Collect and Pay Over Tax, or Attempt to Evade or Defeat Tax