Retro Pay Calculator
A backdated raise owes more than the rate difference on every hour. See the full amount, the overtime true-up the FLSA requires, and what withholding leaves you.
Retro pay is supplemental wages, so it is withheld at a flat 22% federal rate rather than your own rate. Your return settles the difference.
Retro pay (retroactive pay) is money you already earned but were not paid, usually because a raise was approved with an effective date that had already passed. You are owed the difference between the old rate and the new one for every hour worked since that effective date — and, if any of those hours were overtime, 1.5× the difference on those, because a backdated raise raises the regular rate the overtime premium is built on.
How to calculate retro pay
The third line is the one that goes missing. Most retro calculators — and plenty of payroll runs — compute the difference against all hours and stop, which underpays by half the difference on every overtime hour.
The overtime true-up almost everyone skips
The Department of Labor’s regulation on retroactive increases is unusually direct about this, and it settles the question with its own arithmetic:
“Where a retroactive pay increase is awarded to employees … it operates to increase the regular rate of pay of the employees for the period of its retroactivity. Thus, if an employee is awarded a retroactive increase of 10 cents per hour, he is owed, under the Act, a retroactive increase of 15 cents for each overtime hour he has worked during the period, no matter what the agreement of the parties may be.”
— 29 CFR 778.303
Ten cents becomes fifteen because overtime hours are paid at 1.5× the regular rate, and the regular rate itself just went up. The last clause matters too: this is not negotiable between you and your employer, and a lump-sum retro payment does not escape it — a lump sum has to be prorated back across the hours of the period it covers (29 CFR 778.209) and the overtime recomputed from there.
Worked example
A raise from $22.00 to $23.50 takes effect on 1 June, but payroll does not apply it until 1 August. In those eight weeks you worked 320 regular hours and 40 overtime hours.
The difference is $1.50/hour. Regular hours owe 1.50 × 320 = $480.00. Overtime hours owe 1.50 × 1.5 × 40 = $90.00. Retro pay owed: $570.00.
A calculator that multiplied $1.50 by all 360 hours would say $540.00 — $30.00 short, which is exactly half the difference on each of the 40 overtime hours.
Retro pay on a salary
For an exempt salaried employee there is no overtime true-up, because there is no overtime premium to true up. The math is the per-paycheck difference times the number of checks that went out at the old figure:
A raise from $60,000 to $64,000 on biweekly pay is $4,000 ÷ 26 = $153.85 per check; five checks at the old figure means $769.23 in retro pay. If you are salaried but non-exempt — salaried and still entitled to overtime — use the hourly mode instead, with your regular rate worked out from the salary.
Why the check is smaller than the number above
Retro pay is supplemental wages. IRS Publication 15 lists “back pay” and “retroactive pay increases” by name alongside bonuses and commissions, which means that if it is paid as its own check your employer may withhold federal income tax at a flat 22% instead of running it through your W-4. Two consequences:
- It is a withholding rate, not a tax rate. If your marginal rate is 12%, the 22% is over-withholding and the excess comes back as refund. If you are in the 24% bracket or higher, it under-withholds and you settle the rest at filing.
- Everything else still applies. Social Security and Medicare come out normally, as does state withholding — and a few states set their own supplemental rate (California 10.23%, New York 11.70%) rather than using their ordinary tables.
If the retro amount is instead folded into a regular paycheck without being identified separately, your employer withholds on the combined total as if it were one ordinary period — which usually withholds more, because a single large check looks like a much larger annual income to the withholding tables.
Quick reference: retro pay per 100 hours
| Raise | 100 regular hours | 100 overtime hours | Extra from the true-up |
|---|---|---|---|
| $0.25/h | $25.00 | $37.50 | $12.50 |
| $0.50/h | $50.00 | $75.00 | $25.00 |
| $1.00/h | $100.00 | $150.00 | $50.00 |
| $1.50/h | $150.00 | $225.00 | $75.00 |
| $2.00/h | $200.00 | $300.00 | $100.00 |
| $3.00/h | $300.00 | $450.00 | $150.00 |
When retro pay comes up
- A raise processed late. The most common case: approved in March, effective 1 January, first appears on the April check.
- A union contract settled after it started. Collective bargaining agreements are routinely ratified months into their term, with the new scale backdated — this is the situation 778.303 was written for.
- A misclassified or mis-keyed rate. Payroll entered $18.00 instead of $18.50; every hour since owes the difference.
- Overtime that was calculated on the wrong regular rate — for example a shift differential or a non-discretionary bonus that should have been folded into the regular rate and was not.
- A promotion with a backdated effective date, where the title changed on one date and the pay grade on another.
Retro pay is not the same as back pay in the legal sense, though the words get used interchangeably. Back pay in a wage claim or a settlement is compensation for wages wrongfully withheld and can carry interest and liquidated damages; retro pay is ordinary payroll catching up with a decision that was already made.
Frequently asked questions
How do I calculate retro pay?
Subtract the old rate from the new rate, then multiply by the regular hours worked since the effective date. Add 1.5 × the difference for every overtime hour in that period. For a raise from $22.00 to $23.50 across 320 regular and 40 overtime hours: (1.50 × 320) + (1.50 × 1.5 × 40) = $480 + $90 = $570.
Does a backdated raise change the overtime I was already paid?
Yes. 29 CFR 778.303 says a retroactive increase raises your regular rate for the entire retro period, so overtime hours already paid at 1.5× the old rate are owed 1.5× the new one. The regulation adds that this applies “no matter what the agreement of the parties may be” — an employer and employee cannot agree to skip it.
Why was so much tax taken out of my retro check?
Retro pay is supplemental wages under IRS Publication 15, section 7, so when it is paid as a separate check your employer may withhold federal income tax at a flat 22%. That is a withholding rate, not your tax rate — if your marginal bracket is 10% or 12%, the excess comes back as refund when you file.
How is retro pay calculated for a salaried employee?
Divide the annual increase by the number of paychecks in a year to get the per-period difference, then multiply by the number of checks issued at the old figure. A $60,000 → $64,000 raise on biweekly pay is $153.85 a check; five late checks is $769.23. Exempt salaried employees get no overtime true-up; salaried non-exempt employees do.
How long does an employer have to pay retro pay?
There is no single federal deadline for the retro amount itself, but the underlying wages are subject to the FLSA’s two-year statute of limitations for recovery (three years for willful violations), and most states require wages to be paid on the regular payday for the period in which they are earned. In practice retro pay appears on the next scheduled payroll after the change is processed.
Is retro pay the same as back pay?
Not quite. Retro pay is payroll catching up on a rate change that was already approved. Back pay is wages you should have received but did not — often the subject of a wage claim or settlement, and it can carry interest and liquidated damages. The tax treatment is the same: IRS Publication 15 names both as supplemental wages.
Official sources
Every rate and threshold on this page comes from the issuing agency. Verify anything here against the primary source:
- 29 CFR 778.303 — Retroactive pay increases — a retroactive increase raises the regular rate for the whole period; the regulation’s own example owes 15 cents for every overtime hour on a 10-cent raise
- 29 CFR 778.209 — Method of allocating bonuses — how a lump-sum retro payment is prorated back over the hours of the period it covers
- IRS Publication 15 (2026), section 7 — Supplemental Wages — “back pay” and “retroactive pay increases” are named supplemental wages: optional flat 22% withholding, mandatory 37% above $1,000,000 a year
- U.S. Department of Labor — Overtime Pay — the time-and-a-half requirement over 40 hours in a workweek that the true-up recomputes
- 29 U.S.C. 255(a) — Statute of limitations — unpaid-wage actions must be commenced within two years, or three for a willful violation
- SSA — Social Security wage base — 2026 taxable maximum of $184,500, past which retro pay stops paying the 6.2% share
Last reviewed: 2026-09-11 · Report an issue