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If you have a pay stub open right now and you are stuck on short codes like FITW, OASDI, MED, REG, or PTO, you are not alone. Pay stubs cram a lot of information into small boxes, so payroll systems shorten labels into abbreviations.

Two important things to know before you start:

1. Most pay stub abbreviations are common across employers, but some are payroll-provider or employer-specific.
2. The fastest way to decode a code is not to Google the code alone. It is to identify the section it appears in and what it changes (gross pay, taxable wages, or net pay).

This guide gives you a simple “decode in 60 seconds” method, a large master lookup table, real-world examples, and troubleshooting for the most common “why did my net pay change?” situations.

Disclaimer (please read): This article is general information. Pay stubs, benefit plans, and state rules vary. If you do not recognize a code, ask your HR/payroll team for the official meaning and whether it is pre-tax, post-tax, or informational.

Quick answer: the 60-second pay stub decoding method

• Step 1: Find the section: Earnings, Taxes, Deductions, or Employer Paid.
• Step 2: Check the column: Current vs YTD (year-to-date).
• Step 3: Ask what it affects: Gross, Taxable wages, Net pay, or Info-only.
• Step 4: Compare wage bases: taxable wages may be lower than gross because of pre-tax deductions.
• Step 5: Confirm plan-dependent items: some benefits and disability lines can be pre-tax or post-tax depending on how the plan is set up.

If you do those five steps, most “mystery codes” stop being mysterious.

Why pay stubs use abbreviations (and why they differ)

Payroll software uses short labels because:

• Field names are limited in length
• Many earnings/deductions are stored as internal codes
• Employers customize categories (especially benefits)

So REG almost always means regular pay, but something like DED1 or BEN2 may be an internal label that only your employer can explain.

Before you look up a code: understand the four pay stub “buckets”

1) Earnings (build your gross pay)

These lines add up to GROSS pay.

2) Taxes (withheld from your check)

These reduce your take-home pay and are sent to tax agencies.

3) Deductions (benefits, retirement, garnishments, etc.)

These may be pre-tax (reduce certain taxable wages) or post-tax (reduce net only).

4) Employer-paid items

Some stubs list what the employer pays on your behalf. These often do not reduce your net pay.

The “tax basics you can trust” box (simple and accurate)

Most pay stubs show two different kinds of tax-related lines:

• Income tax withholding (like federal income tax withholding, and sometimes state/local withholding)
• Payroll taxes for Social Security and Medicare (often shown as OASDI/SS and MED/HI)

You may also see unemployment-related items (FUTA, SUTA/SUI) which are commonly employer-paid, though a few states require employee contributions. If you are unsure whether an unemployment line is a withholding or informational, payroll can confirm.

Three mini-examples that make pay stub codes “click”

Example 1: Gross vs taxable wages vs net (simple numbers)

Imagine your pay stub shows:

Earnings

• REG: $1,000.00
• GROSS: $1,000.00

Pre-tax deductions

• 401K: $100.00
• MED INS: $50.00

Now federal taxable wages might be lower than gross:

• $1,000.00 − $100.00 − $50.00 = $850.00 (taxable wages for federal income tax in many setups)

Taxes

• FITW: $90.00
• OASDI: $62.00
• MED: $14.50

Post-tax deductions

• UNION: $10.00

Net pay

• $1,000.00 − $100.00 − $50.00 − $90.00 − $62.00 − $14.50 − $10.00 = $673.50 NET

What this teaches: Gross pay can stay the same while taxable wages and net pay change because of pre-tax deductions.

Example 2: Traditional 401(k) vs Roth (why withholding can differ)

Two people each contribute $100 to retirement:

• Person A contributes 401K (traditional). This is often pre-tax for federal income tax.
• Person B contributes ROTH. This is typically post-tax.

Both save $100, but Person A may see slightly lower federal withholding because taxable wages are reduced.

What this teaches: Not all retirement lines affect taxable wages the same way.

Example 3: “Mystery code” walkthrough (how to stop guessing)

Your net pay dropped this period. You see:

• REG looks normal
• New deduction: LTD
• One-time line: RETRO

How to decode:

1. Section check: LTD appears in Deductions → likely a benefit premium.
2. Taxable wages check: If taxable wages dropped compared to last check (with similar gross), LTD may be pre-tax. If taxable wages did not change, it may be post-tax.
3. RETRO clue: Retro lines often mean a correction (missed deduction catch-up, pay rate correction, or benefit change applied late).
4. Next step: Ask payroll: “What is LTD on our plan, and is RETRO correcting a past period?”

What this teaches: One new benefit + one correction can explain a “random” net pay change.

Common mistakes (and why your net pay changed)

If your paycheck looks different and you want the quickest explanation, start here. These are the most common reasons net pay changes even when your schedule feels the same:

1) Your federal withholding changed (FIT/FITW moved)

Reasons include:

• You updated your withholding settings
• You had a raise (higher taxable wages)
• A bonus or commission was included
• Pre-tax deductions changed (changing taxable wages)

Quick check: Compare this pay period’s taxable wages to last pay period’s taxable wages. If taxable wages changed, withholding often changes too.

2) A benefit premium started or changed (MED/DEN/VIS, LTD/STD)

Common triggers:

• New plan year or renewal
• Waiting period ended
• Coverage level changed (self → family)
• A correction applied late (retro)

Quick check: Look for a new line under Deductions, or a sharp increase in the benefit amount.

3) A pre-tax election changed (401K, HSA, FSA)

If you increased your 401(k) or HSA amount, taxable wages may decrease and withholding may shift.

Quick check: If gross is steady but taxable wages dropped, a pre-tax election is a likely cause.

4) Supplemental pay was added (BON, COMM, RETRO)

Bonuses, commissions, and retro pay can change withholding and totals quickly.

Quick check: Scan Earnings for anything besides REG.

5) A garnishment began (GARN, CS, LEVY)

Garnishments reduce net pay and are often large.

Quick check: Look for a brand-new deduction line with those labels.

6) Your hours changed in a way you missed (OT, DIFF, HOL)

Even if total hours are similar, the mix matters:

• Overtime or shift differential can increase gross
• That can increase taxes and change net pay

Quick check: Compare REG hours vs OT hours and any premium lines.

7) Year-to-date totals reset

If you are looking at the first paycheck of a new year, YTD numbers restart.

Quick check: Confirm pay date is early January and you are comparing YTD correctly.

Quick checklist: what to verify every pay period

Use this simple review checklist before you file your pay stub away:

Earnings

• REG hours and rate (if shown) look right
• OT/DIFF/HOL lines match what you worked
• Any bonus/retro/adjustment is expected

Taxes

• FITW + Social Security + Medicare lines look present
• State/local lines appear only if they apply to you

Deductions

• Benefits match your enrollment
• Retirement contributions match your chosen %/amount
• Any new deduction has a clear name and purpose

Totals

• Gross → deductions/taxes → net is reasonable
• Current totals match expectations; YTD increases steadily

FAQs

What does FITW mean on a pay stub?

FITW usually means federal income tax withholding (the federal income tax withheld from that paycheck).

What is the difference between FITW and FICA?

FITW is income tax withholding. FICA generally refers to payroll taxes for Social Security and Medicare.

What does OASDI mean?

OASDI is the Social Security portion of payroll taxes (often labeled OASDI or SS).

Why does my pay stub show Medicare separately?

Many stubs list Medicare as its own line (MED or HI) because it is a separate payroll tax.

What does YTD mean?

Year-to-date: totals from the start of the year through the current pay period.

Why are my taxable wages lower than gross pay?

Pre-tax deductions (like some benefits or traditional retirement contributions) can reduce taxable wages.

What does SUTA/SUI mean?

It relates to state unemployment. Often it is employer-paid and informational, but some states require employee contributions. Payroll can confirm how your stub treats it.

What does RETRO mean?

Retro pay is a correction applied now for a prior period (pay or deductions).

What should I do if I do not recognize a code?

Do not guess. Ask HR/payroll for the full name, whether it is pre-tax or post-tax, and whether it is one-time or recurring.

A soft next step: create a clean pay stub you can actually understand
If you are tired of confusing codes and messy line items, a clear pay stub layout makes everything easier to verify for rentals, loans, and personal records. When you create a pay stub, focus on:

• Clear pay period and pay date
• Itemized earnings (REG, OT, bonus, etc.)
• Separate tax lines (FITW, OASDI/SS, MED)
• Deductions labeled as pre-tax or post-tax when applicable
• Consistent Current and YTD totals

If you want to create a pay stub with clean, readable line items, you can use ePayStubs here: epaystub