Retroactive Pay Calculator

How to Calculate Retroactive Pay

Retroactive pay is the gap between what you were paid and what you should have been paid for work you already did. The math depends on whether you are paid hourly or on a salary.

For hourly workers, take the difference between your new and old hourly rate, then multiply by the hours you worked at the old rate. Overtime hours are handled separately, valued at time-and-a-half of both rates. If your rate went from $20 to $22 and you worked 160 hours at the old rate, your retro pay is ($22 - $20) x 160 = $320 gross.

For salaried workers, divide each annual salary by the number of pay periods per year to get the per-period pay, then multiply the per-period difference by the number of pay periods you were paid at the old rate. A jump from $60,000 to $63,000 on biweekly pay (26 periods) is a per-period difference of about $115.38. Across 3 affected pay periods, that works out to roughly $346.15 gross retro pay.

How Retro Pay Is Taxed in 2026

The IRS treats retro pay as a supplemental wage (Publication 15, Section 7), the same category as bonuses and commissions. When an employer pays retro pay as a separate check, they usually withhold federal income tax at the flat 22% supplemental rate. When retro pay is bundled into a regular paycheck, employers may instead use the aggregate method, which combines it with your normal wages.

This calculator gives you two estimates. The supplemental flat option applies 22% federal withholding. The regular wage estimate applies a flat 12% proxy as a lower-bound figure, since a one-off retro amount added to a single paycheck rarely shifts your tax bracket by much. Either way, Social Security (6.2%) and Medicare (1.45%) apply, and so does any state income tax.

Remember that withholding is not your final tax bill. Retro pay counts as ordinary income when you file your return, and any difference between what was withheld and what you actually owe gets settled then. Supplemental wages above $1,000,000 in a year are withheld at 37% on the excess, which this lightweight tool does not cover.

Retro Pay vs. Back Pay

The two terms often get used interchangeably, but they describe different situations. Retro pay corrects a wrong rate for work that was already paid, just at the wrong amount, for example when a raise was approved but applied late. Back pay covers wages you were owed but never received at all, such as after a wrongful termination, a missed paycheck, or an unpaid suspension.

Put simply, retro pay fixes a rate that was too low, while back pay fills a gap where you were paid nothing. Both are taxable wages, and both are subject to federal, FICA, and state withholding.

Common Reasons Employees Are Owed Retro Pay

Retro pay shows up more often than most workers realize. The usual causes include:

• Delayed raises: a raise approved with an earlier effective date than the paycheck that reflects it. Our Pay Raise Calculator helps you confirm the new rate.
• Missed shift differentials: night, weekend, or hazard pay that was not applied to the right shifts.
• Payroll errors: a wrong rate entered in the payroll system, or a promotion not processed on time.
• Misclassified overtime: overtime hours paid at straight time instead of time-and-a-half.
• Contract or union settlements: negotiated rate increases applied retroactively to a prior date.

Because retro pay is taxed as a supplemental wage, the same withholding mechanics apply to related payouts. Compare with our Bonus Tax Calculator and Severance Pay Tax Calculator. If you are an employer who wants an employee to net a target retro amount, the Gross-Up Calculator works the math backward.