Why Paystub Deductions Change Between Pay Periods

Paystub deductions change between pay periods for four main reasons. Gross pay changed, so percentage-based lines such as Social Security, Medicare, income tax and 401(k) moved with it. A date passed, such as open enrollment or the Social Security wage base. An order or election started or stopped. Or payroll corrected an earlier stub.

Most changes can be explained from the stubs themselves once you know which lines are flat amounts and which are percentages. The sections below sort the causes, work two examples with made-up figures, and give a way to check deduction totals without rebuilding anyone's payroll calculation. For a tour of what each deduction is in the first place, start with paystub deductions explained.

Lines that move with the size of the paycheck

Percentage-based deductions rise and fall with gross pay. Social Security and Medicare are fixed percentages of FICA wages, a 401(k) set as a percentage follows eligible pay, and income tax withholding climbs faster than pay because the withholding tables are progressive. A week with overtime, a commission payout, unpaid leave or a short first paycheck moves all of them together.

Flat deductions ignore the size of the check. A $60.00 medical premium stays $60.00 whether gross pay is $1,200 or $2,000, so when a flat line changes, look for a date or an event instead of a pay difference.

Illustrative example (made-up figures): an hourly employee earning $22.00 an hour works a standard 80-hour biweekly period, then a period that adds 6 overtime hours at $33.00. They defer 4% of gross pay to a traditional 401(k) and pay a $60.00 medical premium through a cafeteria plan. The federal income tax figures are assumptions, not results from IRS tables.

Gross pay rose by $198.00, yet net pay rose by only $150.93, because four of the five deduction lines grew as well. The Social Security base is $1,700.00 in the first period and $1,898.00 in the second, since the cafeteria-plan premium is excluded from FICA wages.

Related: 401k on a Paystub: Traditional vs Roth Deduction Lines

Related: Workers' Comp Payroll Deductions: Who Pays the Premium?

Lines that change on a date

Some deductions stay put for months and then shift on a predictable day:

• Plan year start. New premiums and benefit elections from open enrollment usually take effect when the plan year begins, which for many employers is January 1.
• End of a waiting period. A new hire's first stubs may show no medical line at all, followed by a premium once coverage begins.
• The Social Security wage base. IRS Publication 15 sets the 2026 base at $184,500. Once year-to-date Social Security wages reach it, the line stops until the next calendar year.
• The Additional Medicare Tax threshold. Employers add 0.9% to the Medicare line for wages above $200,000 in the calendar year.
• Annual contribution limits. A 401(k) deferral stops when an employee reaches the plan's yearly limit, which the IRS sets each year.
• Third-paycheck months. Some employers take monthly premiums from only two biweekly paychecks per month, so a month with three paydays has one stub without the premium. The calendar pattern behind this is laid out in biweekly vs semimonthly paystubs.

Illustrative example (made-up figures): a salaried employee is paid $9,000.00 on each of 24 semimonthly pay dates in 2026, with no pre-tax deductions that reduce FICA wages. The last five paychecks of the year look like this.

On the 21st paycheck only $4,500.00 of wages remain under the $184,500 base, so Social Security is $4,500.00 × 6.2% = $279.00. The 23rd paycheck carries wages $7,000.00 past $200,000, so Medicare becomes $9,000.00 × 1.45% plus $7,000.00 × 0.9%, which is $130.50 + $63.00 = $193.50. By the 24th paycheck every dollar is above the threshold: $9,000.00 × 2.35% = $211.50.

Lines that start, stop or jump because of an event

Event-driven changes are the ones most worth confirming, because nothing about the pay period predicts them:

• A garnishment or child support order begins, is modified or is released.
• The employee submits a new Form W-4, changing federal income tax withholding from the next payroll onward.
• A marriage, birth or loss of other coverage allows a mid-year benefit change.
• The employer collects premiums that were missed during unpaid leave, often spread over a few paychecks.
• Payroll recovers an overpayment or refunds an over-deduction, sometimes as a negative amount.
• A bonus in the period is withheld at a flat supplemental rate, which can make the income tax line look out of step; the guide to bonus pay on a paystub shows both withholding methods.
• The employee moves to a different state or city, adding or removing state and local lines.

Matching each change to its evidence

Every legitimate change has a document behind it. The table pairs the usual causes with the lines they move and the record that confirms them.

When the pre-tax status of a deduction changes, taxable wages move too, which in turn shifts tax lines that the employee did not touch. The mechanics are covered in pre-tax vs post-tax deductions.

Checking deduction totals without recalculating payroll

You do not need withholding tables to test whether a deductions section hangs together. These checks use only the numbers printed on two consecutive stubs:

1. Add the current deduction lines and compare the sum with the total deductions figure.
2. Subtract total deductions from gross pay, add any reimbursement, and compare the result with net pay and the bank deposit.
3. Set this stub beside the previous one and mark each line whose amount changed.
4. For every flat line that changed, find the date or event from the lists above that explains it.
5. For percentage lines, test the ratio: Social Security divided by FICA wages should sit very close to 6.2% until the wage base is reached, and Medicare close to 1.45% until wages pass $200,000.
6. Roll each YTD figure forward, adding the current amount to the previous stub's YTD.
7. Write down anything still unexplained, with the pay date and the line name, before contacting payroll.

Step 6 catches double charges quickly. If the last stub showed YTD dental of $216.00 and this stub charges $12.00, the new YTD should read $228.00; a figure of $240.00 would point to a second charge or a catch-up worth asking about.

Income tax is the one line these checks cannot confirm, because the correct amount depends on the W-4 and the withholding method the employer uses. A large jump with no change in pay or W-4 is still a fair question.

When a changed deduction needs a question

Some changes should go to payroll or HR in writing rather than wait for the next stub:

• A new line with an unfamiliar code and no enrollment or notice behind it.
• A flat premium that changed outside open enrollment with no life event.
• Social Security still being withheld after YTD Social Security wages have clearly passed the wage base.
• The same deduction taken twice for one period.
• A garnishment that continues after the employee received a release.
• YTD amounts that do not roll forward from the previous stub.

If payroll issues a corrected stub, keep the original and the correction together; correcting a paystub record lists what to retain.

State and local changes that follow the employee

State income tax rates, state disability and paid leave premiums, and local wage taxes are set by state revenue and labor agencies and by cities or school districts, and many of them reset on January 1. A move to another state or city, or a switch between remote and on-site work, can add or remove whole lines mid-year. The relevant state agency publishes each year's rates, and the employer's payroll provider can confirm which jurisdictions apply.

Keeping a series of paystub records consistent

When you prepare consecutive paystub-style records, change a deduction only when a source document says it changed, and carry each period's amount into the YTD fields so they roll forward. On PayStubGo's paystub generator, YTD fields sit alongside the current-period taxes and custom deductions, so each stub can be checked with the same seven steps before you download it.

The checks in this guide test whether a stub is internally consistent; they do not confirm that anyone's withholding is right for their tax situation. PayStubGo formats the amounts you enter and does not calculate or verify them, so questions about correct withholding belong with the employer's payroll department or a tax professional.