We checked the retro pay calculator's federal formula, overtime recompute, withholding rates, modeled state scope, state-rate data, Massachusetts exposure callout, and stated limitations. All checked claims ship as Verified.
This calculator is intentionally narrow. It handles hourly rate-change retro pay, optional overtime recomputation under 29 CFR §778.303, federal supplemental withholding, FICA, no-income-tax states, flat-tax states, and California/New York flat-rate estimates. It does not calculate full bonus allocation, commissions, piece-rate work, bracketed-state W-4 withholding, local New York withholding, Social Security wage-base crossings, or state penalty exposure other than the Massachusetts callout.
2026 rate refresh: Kentucky is updated to 3.5%, North Carolina to 3.99%, Mississippi is added at 4%, and Georgia is updated to 4.99% based on HB 463 signed May 11, 2026. Georgia is the one rate with timing caveat: the older 2026 employer guide still showed 5.19%, but the later governor signing release says HB 463 lowers the rate to 4.99% beginning January 1, 2026.
Ship verdict: the calculator can ship under this fact-check. Recheck state rates annually and whenever a state passes midyear tax legislation.
2 claims
A retroactive rate increase requires the rate difference on all affected hours
§778.303 states that a retroactive pay increase operates to increase the regular rate for the retroactive period.
If the period included overtime, the calculator adds 0.5 x rate difference x overtime hours
The regulation's example supports the extra half-time premium on overtime hours after the straight-time difference is already included.
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The $20 to $22 / 180-hour / 20-OT-hour example produces $380 total retro pay
$2 x 180 = $360 straight-time retro. 0.5 x $2 x 20 = $20 overtime retro. Total = $380.
2 claims
Federal supplemental withholding is modeled at 22%
The calculator uses the flat supplemental withholding method. It discloses that aggregate-method withholding can differ.
Supplemental wages above $1 million are withheld at 37% on the excess, but the calculator does not model that threshold
The out-of-scope statement is correct for the calculator's SMB hourly-worker use case.
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FICA is modeled at 7.65%
Employee Social Security is 6.2% and Medicare is 1.45%, totaling 7.65%.
7 claims
The 2026 Social Security wage base is $184,500
The calculator uses the full 7.65% for typical sub-wage-base workers and discloses that high earners crossing the wage base can see lower actual FICA.
Georgia is modeled at 4.99% for 2026
HB 463 was signed May 11, 2026 and lowers Georgia's state income tax rate from 5.19% to 4.99% beginning January 1, 2026. The DOR employer guide may lag because it was published before or around the change; the tool note tells employers to verify payroll-system updates.
Kentucky is modeled at 3.5% for tax year 2026
Kentucky DOR states that the withholding tax rate is 3.5% for tax year 2026.
North Carolina is modeled at 3.99% for tax year 2026
NC DOR's 2026 withholding tables state that the individual income tax rate for tax year 2026 is 3.99%.
Mississippi is modeled at 4% for 2026
Mississippi DOR states that for tax year 2026, taxable income in excess of $10,000 is taxed at 4%. The calculator models the rate for orientation and should be checked against employer withholding instructions during the next annual refresh.
California is modeled at 6.6% as a regular supplemental-wage estimate
The calculator discloses that California employers may use the aggregate method instead, so the 6.6% result is an estimate.
New York is modeled at 11.7% state-only and excludes NYC and Yonkers local withholding
The tool correctly labels New York as state-only and warns that NYC and Yonkers residents will have additional withholding.
2 claims
The calculator models 9 no-income-tax states at $0 state withholding
Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, and Wyoming are modeled as no state income tax on wages.
The calculator models 13 flat-tax states directly
Modeled flat-tax states are Arizona, Colorado, Georgia, Idaho, Illinois, Indiana, Kentucky, Massachusetts, Michigan, Mississippi, North Carolina, Pennsylvania, and Utah.
4 claims
Other bracketed-rate states are not modeled
The widget uses "Other state — variable rate" for states where withholding depends on W-4-style inputs, bracket tables, residency, or local rules the calculator does not collect.
Bonus-driven retroactive overtime is not modeled
Bonus allocation requires different inputs from a rate-change correction, so the tool correctly sends readers to the article and research.
Salary mode is not modeled
The widget has hourly-rate and hours inputs only.
Multi-state employment is not modeled
The widget accepts one state for the whole correction period.
1 claim
Massachusetts selection surfaces a separate treble-damages exposure amount
The callout is separate from withholding. It shows potential wage-claim exposure if an employee prevails, not the routine net paycheck amount.
1 claim
Reuter held that voluntary payment before suit does not avoid Massachusetts treble damages
The tool note uses this to explain why the exposure row appears even though the calculator is otherwise a withholding tool.
17 unique sources cited across the report — click to audit any claim directly against its evidence.
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