Salary Back Pay Calculator

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A raise that took effect months ago, a payroll error that underpaid you for weeks, or a promotion that never reached your checks: back pay is the difference between what you should have earned and what you were actually paid, over the window where the gap ran. This calculator works both ways pay is quoted, with a per-period Salary mode and an Hourly mode, and shows the per-period or per-hour difference, the total owed, the formula, and a step-by-step breakdown you can attach to a request to payroll.

Salary Back Pay Calculator

Per-period salary mode and hourly mode, with the formula and steps shown for every result

The salary you were actually paid each period.
The salary you should have been paid each period.
How many periods the wrong salary was paid.

Your back pay

Back pay per period
Periods owed

    Quick Answer

    Salary mode is (correct salary per period − previous salary per period) × periods owed: $4,500 − $4,200 = $300 a period, × 6 periods = Total back pay owed: $1800.00, exactly as the pre-filled tool displays it. Hourly mode is the same shape: ($25 − $20) × 80 hours = $400.00. The result is a gross figure, before tax withholding.

    On this page

    How the back pay math works in both modes

    Back pay is always a gap multiplied by a duration. Salary mode computes Back pay per period = Current salary − Previous salary, then Total back pay = Back pay per period × Number of periods. Hourly mode computes Back pay = (Correct hourly rate − Actual hourly rate) × Hours worked.

    Enter per-period amounts in Salary mode, whatever your period is: monthly, semi-monthly, biweekly, or weekly all work, as long as both salary figures use the same period length. If your raise was quoted as an annual figure, divide both annual salaries by your periods per year first (12, 24, or 26). That conversion is the step most people get wrong; guides on how to calculate back pay for a raise walk through the same annual-to-period division before any subtraction happens. If the raise itself is what you are still negotiating, a salary raise calculator helps you model the new figure before it ever becomes a back-pay question.

    Worked example, run through the real tool

    The Salary mode above is pre-filled with this case. A marketing analyst earned $4,200 per month. A delayed promotion made her correct salary $4,500 per month, effective six months before payroll applied it. Enter 4200, 4500, and 6:

    • Step 1: Find the per-period difference: $4500.00 − $4200.00 = $300.00
    • Step 2: Multiply by the number of periods: $300.00 × 6 = $1800.00

    The tool displays Total back pay owed: $1800.00. Note the format: the tool writes money with two decimals and no thousands separator, so the figure appears as $1800.00 rather than $1,800.00. The hourly twin of the same story is pre-filled in Hourly mode: a worker who should have earned $25 an hour but was paid $20 for 80 hours is owed ($25.00 − $20.00) × 80 = $400.00.

    Hourly vs salaried back pay: what changes and what does not

    The formula shape is identical; the evidence is not. Hourly back pay stands on hours, so timesheets and schedules decide the claim. Salaried back pay stands on periods, so the effective date of the change and the date payroll caught up decide it.

    QuestionSalary modeHourly mode
    What you enterOld and correct pay per period, plus periods owedCorrect and actual hourly rates, plus total hours
    Key documentOffer letter or raise memo with the effective dateTimesheets and pay stubs showing hours and rate
    Tricky partConverting annual raises to per-period amountsOvertime hours, which need the premium rate corrected separately
    Mid-window changesCount only periods paid at the old rate; a half period can be entered as 0.5 of a period in your own prorationCount only hours actually paid at the wrong rate

    For overtime, do not blend the hours into one run. The FLSA overtime fact sheet sets the premium at 1.5 times the regular rate past 40 hours a week, so overtime back pay is the gap between the correct and actual overtime rates times the overtime hours. Run it as a second Hourly calculation and add the totals. Workers sorting out a wider pay dispute often also need the unpaid overtime calculator for hours that were never paid at all, which is a different claim from hours paid at the wrong rate.

    Common causes of back pay

    Four patterns produce most cases. Late performance appraisals are the classic one: the raise is approved in March, backdated to January, and the January and February checks stay at the old rate. Payroll keying errors, a wrong hourly rate or a missed shift differential, create the same gap with no raise involved. Promotions and transfers often take effect in the job before they take effect in the HR system. The fourth pattern is legal rather than administrative: minimum-wage or overtime violations, where the Fair Labor Standards Act gives employees a right to recover the unpaid wages, and the Wage and Hour Division recovered back wages for nearly 177,000 workers in fiscal year 2025 alone.

    The mirror-image case exists too. If a correction lowers your rate retroactively, this tool returns a negative total, which reads as an overpayment estimate rather than money owed to you. A pay cut applied on purpose is a separate situation, and the salary cut calculator covers what a reduction does to ongoing pay rather than to a past window.

    What to document before you ask for back pay

    A calculator figure persuades nobody on its own; the paperwork underneath it does. Gather these before you write to payroll, in this order.

    1. The agreement: offer letter, contract, or raise memo naming the correct rate and its effective date.
    2. The shortfall: pay stubs for every affected period showing the rate actually paid.
    3. The duration: timesheets or schedules (hourly) or a period count from the effective date to the correction date (salaried).
    4. The calculation: the step-by-step result from this tool, copied into your email or letter.
    5. The timeline: two or three sentences in your own words: when the change should have started, when it did, and how many periods sit between.

    Employers must keep payroll records for at least three years under the federal recordkeeping rules at 29 CFR Part 516, so a missing stub on your side is rarely fatal; payroll can pull its own copy. If a written request stalls, the next step is a wage claim with your state labor department or the federal Wage and Hour Division. This page gives estimates for planning and documentation; it is not legal, tax, or payroll advice, and deadlines and rights vary by state and contract.

    Taxes and timing: the gross figure is not the deposit

    The total here is gross back pay. When it lands, it is taxed as wages in the year received. The IRS lists back pay and retroactive pay increases as supplemental wages in Publication 15, which gives employers two withholding routes: a flat 22% federal rate when the payment is made separately, or the aggregate method that stacks it on top of a regular paycheck. Either way, Social Security and Medicare withholding also apply, so the deposit will be noticeably smaller than the gross total.

    Timing matters for a second reason: deadlines. An FLSA unpaid-wage claim generally reaches back two years, or three for a willful violation, under 29 U.S.C. Section 216(b), and the same provision allows an equal amount again as liquidated damages in a successful court case. Most documented errors never get near a courtroom, but the clock is a good reason to send the written request promptly. If the dispute is really about how a raise compounds over time rather than a past gap, an hourly raise calculator is the better tool for that forward-looking question.

    What competing calculators miss

    Back-pay tools online tend to be built for one pay structure and one situation. The specific gaps:

    • Hourly-only tools strand salaried staff. Date-driven retro pay calculators ask for an hourly rate and weekly hours, forcing salaried employees to invent an hourly conversion before they can start. This page takes per-period salary figures directly.
    • A single number with no working. Several tools return one total with no per-period difference, no formula, and no steps. A figure you cannot show your working for is hard to attach to a wage claim; every result here prints both steps.
    • No negative-result handling. Most tools silently block or misreport an overpayment case. This one returns the negative total, which is exactly what you need when a correction went the other way.
    • Gross vs net silence. Few competitors mention that the IRS treats back pay as supplemental wages, so users mistake the gross total for the deposit. The tax section above sets that expectation before the money arrives.

    Frequently asked questions

    In the US, yes in effect: back pay is taxed as wages in the year you receive it, not the year it was earned. The IRS treats back pay and retroactive raises as supplemental wages in Publication 15, so your employer may withhold federal income tax at the flat 22% rate when it is paid separately, plus Social Security and Medicare. The gross figure from this calculator is before any of that withholding.

    If the amount reflects an agreed salary, a contract rate, or a legal minimum, generally no. Start with a written request to payroll or HR with your calculation and supporting documents. If that fails, you can file a wage claim with your state labor department or with the US Department of Labor's Wage and Hour Division, which enforces back-pay rules under the Fair Labor Standards Act.

    A negative total means the correct rate you entered is lower than what you were actually paid, which happens with retroactive pay cuts or corrections. The tool shows the negative figure rather than blocking it, so you can see the size of the overpayment. Employers may recover genuine overpayments, but the rules vary by state and usually require notice, so talk to HR and get the corrected calculation in writing before repaying anything.

    It should, but calculate overtime separately. If overtime hours were paid at the wrong base rate, the correction belongs on the overtime premium rate, not the straight rate. Run your regular hours in Hourly mode at the regular rates, then run the overtime hours again at the correct and actual overtime rates (usually 1.5 times), and add the two totals.

    Employers and payroll writers often use the terms interchangeably, and the math is identical: the gap between what you should have earned and what you were paid, over the affected window. Payroll teams usually say retro pay for a raise or correction applied late by agreement, while back pay is the term labor law uses for wages recovered after underpayment, including through a Department of Labor case or a court order under the FLSA.

    Convert the annual figures to per-period amounts first: divide each annual salary by your pay periods per year (12 monthly, 24 semi-monthly, 26 biweekly), then enter those two per-period amounts and the number of affected periods. For example, $58,000 to $61,480 paid biweekly is $2230.77 to $2364.62 a period, a $133.85 difference per period. The tool works in per-period amounts so any pay frequency fits.

    Under the FLSA, an employee generally has two years to bring an unpaid-wage claim, extended to three years for a willful violation, and state laws set their own deadlines that can be shorter or longer. You do not need a court case or an agency investigation: most back pay is settled inside payroll once the error is documented. Because deadlines differ, do not sit on a documented claim; raise it in writing as soon as you have the numbers.

    Not usually. Back pay means wages for work already performed that were paid at too low a rate or not paid when due. An unpaid bonus, a leave payout at separation, and severance are separate final-pay items with their own rules. If several items are owed at once, calculate the wage-rate gap here and handle the other items with payroll separately, so each figure stays defensible.

    The tool formats money with two decimals and no thousands separator, so one thousand eight hundred dollars displays as $1800.00. The value is identical; only the comma is missing. When you copy the result into a letter or wage claim, you can write $1,800.00 in your own text without changing the amount.

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    References

    1. U.S. Department of Labor, Wage and Hour Division. Fair Labor Standards Act (FLSA) (the federal wage law under which most US back pay is owed and enforced). Accessed October 24, 2026.
    2. U.S. Department of Labor, Wage and Hour Division. Workers: Rights and Filing a Complaint (how employees raise unpaid-wage and back-pay claims with the WHD). Accessed October 24, 2026.
    3. Cornell Legal Information Institute. 29 U.S. Code Section 216: Penalties (employee right to recover unpaid wages plus an equal amount in liquidated damages, and the two and three year limits). Accessed October 24, 2026.
    4. U.S. Department of Labor, Wage and Hour Division. Fact Sheet #23: Overtime Pay Requirements of the FLSA (the 1.5 times regular rate rule used for overtime back-pay corrections). Accessed October 24, 2026.
    5. Internal Revenue Service. Publication 15, Employer's Tax Guide (back pay and retroactive raises classified as supplemental wages; 22% flat withholding option). Accessed October 24, 2026.
    6. Internal Revenue Service. Publication 15-T, Federal Income Tax Withholding Methods (how withholding on a lump-sum wage payment is computed). Accessed October 24, 2026.
    7. Internal Revenue Service. Topic No. 751: Social Security and Medicare Withholding Rates (payroll tax withholding that also applies to back pay). Accessed October 24, 2026.
    8. Electronic Code of Federal Regulations. 29 CFR Part 516: Records to Be Kept by Employers (employer payroll record duties, including the three-year preservation rule in section 516.5). Accessed October 24, 2026.
    9. U.S. Department of Labor, Wage and Hour Division. Minimum Wage Laws in the States (state minimum-wage floors that can create back-pay liability above the federal rate). Accessed October 24, 2026.
    10. U.S. Department of Labor. State Labor Offices (state labor department contacts for wage claims). Accessed October 24, 2026.

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