Backdated pay rises: check your arrears and deductions

Suppose a new agreement raises your annual salary from £30,000 to £31,200, effective from 1 April. October is the first month paid at the new rate. You worked the same hours throughout, with six complete months of the increase owed for April to September.

Item	Calculation	Gross amount
Annual increase	£31,200 − £30,000	£1,200
Monthly increase	£1,200 ÷ 12	£100
Arrears for April to September	£100 × 6	£600
October ordinary salary at the new rate	£31,200 ÷ 12	£2,600
October total, including arrears	£2,600 + £600	£3,200

This invented example checks gross-pay arithmetic, not a particular national award or a net-pay result. Compared with the old £2,500 monthly salary, October’s gross is £700 higher: £100 ongoing increase plus £600 arrears. Counting October again in the arrears would double-count that month’s increase.

If your award is a percentage, apply it to the eligible old rate, then check any employer rounding. A 4% rise on £30,000 gives the £1,200 increase above. The agreement may exclude some allowances or set different increases for different pay points.

Make one row for each period with the same pay rate and hours. Record the rate you should have received, the amount already paid and the difference. Then total the differences. This is more useful than dividing a bank-payment increase by the award percentage.

• Changed hours or grade: use the relevant fraction and pay point for each period, not today’s hours for the entire backdated period.
• Part months: ask which contractual daily-rate or working-day method payroll uses.
• Overtime and allowances: check whether the award changes their rate and which hours qualify.
• Unpaid leave or statutory/family leave: ask payroll to explain the effect of the award on those periods instead of assuming every month receives the same increase.

For school support or other part-year work, use the actual contracted salary and applicable weeks. Our term-time-only pay guide explains why the advertised full-time salary can be a different figure.

Backdated employee pay is normally taxable. There is no separate “back-pay tax rate”. The important timing question is when you were entitled to receive it. Under HMRC’s backdated-pay guidance, employment earnings are generally taxed at the earlier of payment and entitlement to receive them.

Situation	What to check
A newly agreed pay rise applies retrospectively	The agreement and date the extra money became payable; the earlier work dates alone do not move the tax into an earlier year
Wages already due under the existing contract were paid late	The original date they were payable; an earlier tax year may be involved

For example, ordinary March wages due in March but delayed until April are different from a new award first payable in April that covers work done in March. Ask payroll to identify the entitlement and payment dates if the amount crosses 5 April. Do not assume every arrears payment belongs entirely to the year the money reaches your bank.

PAYE deducted on the payslip is also affected by your code, tax basis and pay history. Cumulative PAYE takes earlier pay and tax in the tax year into account; M1/W1 treatment considers the current pay period separately. A high deduction does not prove an error, and a later refund is not guaranteed. Scotland has different income-tax bands; check the country and code used.

Employee National Insurance: for an ordinary payment while you remain employed, HMRC says arrears are added to other earnings in the pay period and NI is assessed on the total. Payroll does not simply divide the extra payment across the old months for NI because it relates to those months.

Student and postgraduate loans: a larger pay period can trigger or increase a deduction. SLC’s refund rules include repayments where total annual income was below the applicable threshold, checked after that tax year ends. Uneven pay alone does not establish a refund entitlement. Check your plan and the relevant year rather than assuming PAYE and loan repayments reconcile in the same way.

Pension: ask which arrears are pensionable, which scheme rules and contribution rate apply, and how they appear on the payslip. A pension adjustment can reduce the cash increase without changing the gross arrears owed. Keep employee pension deductions separate from any employer contribution shown for information.

Use our student-loan payslip guide or PAYE and NI comparison for the individual deduction you are checking.

First check whether the pay award covers former employees, the dates you worked and any claim process or deadline. Leaving before the payment date does not answer that contractual question. Ask your former employer for the award terms and an explanation of your eligibility.

Where a payment is made after your P45, HMRC tells employers to use 0T on a week-1 or month-1 basis, with S0T or C0T where applicable. The employer should provide written payment and deduction details, rather than another P45. Irregular payments after leaving can also use a weekly NI period, so do not expect the deductions to mirror an old monthly payslip.

Keep that statement with your P45 and check the income HMRC records. Our final-payslip guide separates outstanding salary, holiday and other leaving-payment checks.

In the example, £600 of October’s gross pay is one-off. The normal new gross salary is £2,600 a month. Use the pay-rise explorer to compare the old and new annual salaries under the same assumptions; it estimates the ongoing change, not the exact deductions on a lump-sum arrears payslip.

If you receive Universal Credit, a larger earnings payment can affect the monthly assessment period. GOV.UK explains how changing wages affect payments. Check your statement and raise a journal question if the reported earnings or dates are wrong. Do not assume the tax treatment determines the benefit treatment or that the award can automatically be spread over earlier months.

Compare the month before, the arrears month and the next normal month. Our payslip comparison tool helps you separate earnings from deductions; it does not decide which historical amounts your employer owes.

“Please show the old and new rates, the effective date, the dates and hours included, and the gross arrears for each period. Which allowances and pensionable amounts changed? Please also confirm the tax-year treatment and PAYE basis, NI period, loan plan and any payment-after-leaving treatment.”

Start with the disputed line and a specific period. If gross arrears are wrong, payroll needs the award and work-history evidence. If the amount is correct but the tax code or HMRC income record is wrong, follow the tax-code checks. Do not send a complete payslip to a public forum: a redacted line-by-line question is usually enough to explain the issue.