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Retroactive Pay Calculator

Enter the old and new pay per period and periods owed to get the back pay.

Result

$1,400.00

How it is calculated

The formula is back pay = (new pay − old pay) × periods. Pay is the amount for one pay cycle (one month, two weeks, one week), and the old and new figures must use the same cycle. Periods is the number of cycles that were paid at the old rate after the raise should have started. It can be a fraction for a partial cycle, so 2.5 means two and a half cycles. All three numbers must be zero or higher; a negative entry gives no result. The result is a plain difference in dollars, so it is a gross figure: income tax, social security and other deductions are not applied. If the new pay is lower than the old, the result is shown with a minus sign, for example -$1,400.00, which is an overpayment rather than money owed.

Worked example

An employee's monthly pay was 3,800 and a raise to 4,150 was agreed, but payroll applied it four months late. The difference per period is 4,150 − 3,800 = 350. Multiplied by the 4 cycles paid at the old rate, back pay = 350 × 4 = $1,400.00. If the delay had covered two and a half cycles, the same raise would give 350 × 2.5 = $875.00. These are before-tax amounts, and payroll withholds on them as usual.

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Common mistakes

  • Counting periods from the date the raise was announced instead of the date it took effect. Only cycles paid at the old rate after the effective date count.
  • Mixing pay cycles, such as an old monthly salary with a new weekly one. Convert both to the same cycle before entering.
  • Including the pay period in which the raise was already applied. That cycle was paid correctly and adds nothing to the owed amount.
  • Expecting the result to be the net amount you will receive. It is gross, and tax and deductions are taken out afterwards.
  • Entering old and new pay in the wrong order. Swapped, the result turns negative and looks like an overpayment.

About this calculator

Retroactive pay ("back pay") is the difference owed to an employee when a raise, promotion, or new contract rate is applied later than the date it actually took effect. It's calculated simply as the per-period pay difference (new rate minus old rate) multiplied by the number of pay periods that were shorted — for example, a $200/month raise that took three payroll cycles to process owes $600 in retro pay.

Payroll and HR departments run this calculation constantly after union contract ratifications (which are often retroactive to the contract's start date), government pay-scale adjustments, and delayed performance-review raises, since labor law in most jurisdictions requires the shortfall to be paid out rather than absorbed going forward.

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