Retro Pay Calculator — Back Pay Owed on a Raise
Retro pay is the money you are still owed when a raise or a corrected rate is applied backwards to work you already did. The formula is the difference between the new rate and the old rate, multiplied by the hours you worked at the old rate, with overtime hours recalculated at 1.5 times that difference. Enter both rates and how many pay periods were affected, and the calculator shows the gross back pay, the overtime portion, and an estimated net check.
Withholding estimate uses the IRS flat 22% supplemental wage rate plus 7.65% Social Security and Medicare. State and local tax are not included.
How retro pay is calculated
Retroactive pay is the gap between what you were paid and what you should have been paid, added up over every pay period the wrong rate was used. The arithmetic is the same no matter the cause:
- Find the per-hour or per-period shortfall: new rate minus old rate.
- Multiply by the hours (or pay periods) the old rate covered.
- Recalculate any overtime in those weeks at the corrected regular rate. This step is the one most often skipped.
Written out: Retro pay = (new rate − old rate) × hours worked at the old rate, plus (new rate − old rate) × 1.5 × overtime hours for non-exempt workers.
Worked example
A maintenance electrician gets a raise from $30.50 to $33.00 an hour, approved in June but backdated to the first pay period in April. Six biweekly periods have already been paid at the old rate, each with 80 regular hours and 6 overtime hours.
- Hourly difference: $33.00 − $30.50 = $2.50
- Regular retro: $2.50 × 80 hours × 6 periods = $1,200.00
- Overtime retro: $2.50 × 1.5 × 6 hours × 6 periods = $135.00
- Gross retro owed: $1,335.00
Skipping the overtime step would have short-changed that electrician $135. Electricians earn a median of $63,190 a year and reach $140,340 at the top of the range in California, per BLS OEWS May 2025 — and much of that upper range is overtime-driven, which is exactly why the overtime recalculation matters.
How retro pay is taxed
Retro pay is a supplemental wage. When it is paid as a separate check, employers commonly withhold federal income tax at the flat 22% supplemental rate, plus 7.65% for Social Security and Medicare, plus any state and local tax. That is withholding, not your final tax bill — if 22% is higher than your actual bracket, the difference comes back at filing. If the retro is folded into a regular paycheck, the aggregate method is used instead and withholding often looks even steeper for that one check.
When retro pay applies
- Backdated raises. The increase is approved in month three but effective from month one.
- Union contract settlements. A new agreement is ratified months after the old one expired, with the new scale effective from the expiration date.
- Missed shift or role differentials. Night, weekend, hazard, bilingual or charge-nurse premiums that were never coded into payroll.
- Promotion effective dates. You started the new job before the paperwork caught up.
- Payroll errors. A wrong rate keyed at hire, a step increase that never fired, misclassified overtime.
Common mistakes
- Forgetting overtime. Under the FLSA, raising the regular rate raises the overtime rate for the same weeks. Retro on straight time only is incomplete.
- Counting pay periods instead of weeks worked. If you were on unpaid leave for part of the window, those hours were never paid at the old rate, so there is nothing to make up.
- Confusing retro pay with back pay. Retro pay corrects a rate that was too low. Back pay covers wages never paid at all — missed checks, unpaid final wages, hours worked off the clock.
- Assuming the 22% withholding is the tax. It is an advance payment, reconciled on your return.
- Ignoring the effect on benefits. Retro pay usually counts toward the year it is paid for retirement contributions and pension credit, but plans differ. Ask before assuming.
Frequently Asked Questions
Related job pages
Backdated raises and contract settlements are most common in union and public-sector jobs. These pages carry the current wage range for each one.
Wage figures above are the national median for each job from the U.S. Bureau of Labor Statistics, Occupational Employment and Wage Statistics, May 2025.