Most gross-to-net questions that get marked wrong are not marked wrong for arithmetic. They are marked wrong because two steps were swapped. Here is the order payroll actually runs, why each rung depends on the one above it, and the single place where two different taxable-wage figures appear on the same paystub.
A paycheck is not a pile of subtractions you can do in any sequence. It is a ladder, and every rung depends on the one above it.
Almost every gross-to-net question that gets marked wrong is marked wrong because two steps were swapped, not because anyone fumbled the arithmetic. Here is the order.
| Step | What happens | Depends on |
|---|---|---|
| 1 | Gross pay | Hours, rate, salary, bonuses |
| 2 | Pre-tax deductions | Gross pay |
| 3 | Taxable wages | Gross less pre-tax deductions |
| 4 | Federal income tax | Taxable wages for income tax |
| 5 | Social Security tax | Taxable wages for FICA |
| 6 | Medicare tax | Taxable wages for FICA |
| 7 | Post-tax deductions | What is left |
| 8 | Net pay | Everything above it |
Steps 4, 5 and 6 do not always use the same number. There are two taxable-wage figures on a paystub, not one, and they part company the moment a retirement deferral appears. That is step 3, and it is the subject of a whole separate guide.
Put a deduction one rung too high and you understate every tax below it. Put it one rung too low and you overstate them. The employee's net pay comes out wrong in both directions, and so does the employer's deposit.
A worked example makes it concrete. Dana earns $78,000 a year, paid semi-monthly. She has a Section 125 medical premium of $145.00 per period and a post-tax life insurance premium of $40.00. Her employer's withholding tables produce $286.00 of federal income tax this period.
| Rung | How it is built | Amount |
|---|---|---|
| Gross pay | $78,000.00 ÷ 24 periods | 3,250.00 |
| Pre-tax deductions | Section 125 medical premium | 145.00 |
| Taxable wages | $3,250.00 − $145.00 | 3,105.00 |
| Federal income tax | From the withholding tables | 286.00 |
| Social Security tax | $3,105.00 × 6.2% | 192.51 |
| Medicare tax | $3,105.00 × 1.45% | 45.02 |
| Post-tax deductions | Life insurance premium | 40.00 |
| NET PAY | 2,541.47 | |
Now move one thing. Treat that $145.00 medical premium as post-tax instead of pre-tax and taxable wages become $3,250.00. Social Security becomes $201.50 and Medicare becomes $47.13 — the employee is over-taxed by $11.10 on a single cheque, the employer's matching side is wrong by the same amount again, and nothing about the arithmetic was difficult. Only the order was wrong.
Before any of the above, gross pay has to be right, and the most common way it is not is a pay-frequency mix-up. Semi-monthly means twice a month — 24 periods a year. Bi-weekly means every two weeks — 26 periods a year, and 27 in some years depending on how the paydays fall.
On a $78,000 salary that is $3,250.00 per period against $3,000.00 per period. Every rung below it inherits the error.
| Frequency | Periods | Gross per period |
|---|---|---|
| Weekly | 52 | 1,500.00 |
| Bi-weekly | 26 | 3,000.00 |
| Semi-monthly | 24 | 3,250.00 |
| Monthly | 12 | 6,500.00 |
A deduction is pre-tax only if a specific provision of law says it is. There is no general principle that benefits come out first. When you cannot remember, the question to ask is which taxes does this particular provision exempt the money from — because the answer is often “some, not all”.
| Deduction | Income tax | Social Security & Medicare |
|---|---|---|
| Section 125 health, dental, vision premiums | Exempt | Exempt |
| Section 125 flexible spending account | Exempt | Exempt |
| Traditional 401(k) elective deferral | Exempt | NOT exempt |
| Roth 401(k) contribution | Not exempt | Not exempt |
| Union dues | Not exempt | Not exempt |
| Wage garnishment | Not exempt | Not exempt |
| Charitable payroll deduction | Not exempt | Not exempt |
Read the 401(k) row again. It is the only line in that table where the two columns disagree, and it is the reason a paystub can carry two different taxable-wage figures.
Both FICA taxes are a percentage of a dollar amount, so both produce fractions of a cent constantly. Dana's Medicare is $3,105.00 × 1.45% = $45.0225, which rounds to $45.02. A cent either way is the difference between a right answer and a wrong one on a multiple-choice exam, because the wrong roundings are usually sitting there as distractors.
Round once, at the end of each tax calculation — not at every intermediate step. Rounding the taxable wage figure first, then applying the rate, will drift you off the published answer often enough to cost you questions.
A finished paycheck has to foot in both directions. Gross, less every deduction and every tax, equals net. If it does not, the error is somewhere above the bottom line, and the fix is to walk back up the rungs rather than to adjust net pay until it looks right.
For Dana: $3,250.00 − $145.00 − $286.00 − $192.51 − $45.02 − $40.00 = $2,541.47. That is the same figure the table produced, arrived at a different way, which is the only kind of check worth doing.
Gross pay, then pre-tax deductions, then taxable wages, then federal income tax, then Social Security tax, then Medicare tax, then post-tax deductions, then net pay. Each step depends on the one above it. Moving a deduction between the pre-tax and post-tax positions changes every tax calculated below it.
Twenty-four. Semi-monthly means twice a month. Bi-weekly means every two weeks, which is twenty-six periods a year and occasionally twenty-seven. On a $78,000 salary the difference is $3,250.00 per period against $3,000.00 per period, and every figure below gross pay inherits that error.
It depends on the deduction. A Section 125 cafeteria plan premium reduces wages for federal income tax and for Social Security and Medicare. A traditional 401(k) elective deferral reduces wages for federal income tax only, and does not reduce Social Security or Medicare wages. That difference is why a paystub can show two different taxable-wage figures.
Round to the nearest cent, once, after applying the rate to the taxable wage figure. Do not round the wage figure first. Medicare at 1.45% on $3,105.00 is $45.0225, which rounds to $45.02. Rounding at intermediate steps drifts answers off by a cent or two, and on a multiple-choice exam those near-misses are usually offered as distractors.
A pre-tax deduction comes out of gross pay before tax is calculated, so it lowers the wages that tax is applied to. A post-tax deduction comes out after every tax has already been calculated, so it lowers the employee's take-home pay and nothing else. A deduction is only pre-tax if a specific provision of law makes it so; there is no general rule that benefits come out first.
Reading the order and running the order are different skills, and only one of them is tested. Our practice app has a Gross-to-Net Ladder that walks one paycheck a rung at a time and stops at the first figure that does not balance, which is the opposite of how most practice works — you cannot carry an error downward and still finish.
If you want to know which of the seven content areas is your weak one before spending money on anything, the 20-question assessment is free. No card. It gives you a per-area breakdown. If it tells you Calculation of the Paycheck is fine, that is a useful result too.
The full bank is 570 questions for $69, once, with a written explanation on every question and a 30-day refund if it is not useful. It is not a substitute for PayrollOrg's own materials and does not pretend to be. It is drill.
Take the free 20-question assessment → See the full question bank — $69 once →PUBLISHED 2026-08-08 · ESCHEAT SHEET