Firefighter pay rise back pay: how arrears are calculated

What back pay is and why it happens

Back pay, or arrears, is pay you are owed for a period that has already passed. For firefighters it usually arises from a national pay award. Each award has an effective date, 1 July each year in recent years, but employers can only implement the award in payroll once the agreement has been confirmed and payroll has processed it. If the payroll run happens after 1 July, the extra pay for the earlier months is paid as a lump sum or as a separate arrears line.

The 2026 timeline shows how tight this can be. The FBU consultative ballot concluded on 2 July 2026, the NJC circular is dated 3 July 2026, and London Fire Brigade's policy says implementation and payment of the revised 2026 rates was in July 2026 salaries. In other years the gap was larger: the 7% award for 2022 was confirmed by a circular dated 6 March 2023, eight months after its 1 July 2022 effective date.

The effective date, not the payment date, decides what you are owed. The FBU urged employers to apply the 2026 award to all Grey Book employees as a matter of urgency, and the NJC circular states the rates apply from 1 July 2026. Your contract and your service's implementation notice will confirm the date.

How to calculate your basic pay arrears

Find the annual figure for your role and stage before and after the award. Subtract to get the annual difference, then divide by the number of pay periods in the year: 12 if you are paid monthly, 13 if paid four-weekly. Multiply by the number of periods that were paid at the old rate. For a competent firefighter the annual difference is £40,358 − £38,881 = £1,477.

Monthly: £1,477 ÷ 12 = £123.08 a month. Four-weekly: £1,477 ÷ 13 = £113.62 per period. Weekly: £1,477 ÷ 52.143 = £28.33. If the new rate was implemented in your October pay, and you were paid the old rate for July, August and September, the arrears are 3 × £123.08 = £369.25 gross (£369.24 to £369.25 depending on rounding). A four-weekly employee with three periods at the old rate is owed 3 × £113.62 = £340.86.

The table applies the same method to other pay points. Each figure is the gross annual difference from NJC/3/25 to NJC/2/26 divided by 12, then multiplied by three months, as an illustration. Partial months, unpaid leave and part-time hours change the arithmetic, so use the exact dates on your payslip for your own case.

Overtime, on-call pay, CPD and other linked payments

Basic pay is only one part of the arrears. Anything calculated from the hourly rate also rose from 1 July 2026. A competent firefighter's overtime rate rose from £26.63 to £27.65 an hour, so each overtime hour worked since 1 July at the old rate is owed £1.02. Forty hours of overtime worked before your service applied the award would be £40.80 owed.

For on-call firefighters the retainer, hourly work pay and the disturbance payment all changed: the full retainer for a competent firefighter rose from £5,832 to £6,054 a year (£222, or £18.50 a month), the hourly rate from £17.75 to £18.43 and the disturbance payment from £5.12 to £5.31. A retained firefighter who worked 30 hours and attended 10 calls between 1 July and the implementation date is owed 30 × £0.68 = £20.40 on activity and 10 × £0.19 = £1.90 on disturbance, plus the retainer difference for the months.

CPD payments also rose 3.8% from 1 July 2026. Because CPD is treated as basic pay under the Grey Book, arrears on CPD should be included. Control-room staff at 95% of the firefighting rate get 95% of the same increase. Check that your arrears statement includes every element, not just basic pay. See firefighter overtime rates and on-call firefighter pay.

Tax, pension and National Insurance on arrears

Arrears are pay, so they are subject to income tax and National Insurance through payroll. In most cases they are paid in a single payslip and taxed on the normal cumulative basis for that period, which can make that month's tax look higher even though the total tax for the year is what you would have paid had the rise been paid on time. If you have a different tax code or a student loan, the deduction will follow your usual rules.

Pension contributions are usually deducted on pensionable elements of pay, which include basic pay and CPD under the Grey Book. Whether your service deducts contributions on arrears when they are paid, and how they are recorded on your pension record, depends on your scheme administrator, so ask if you cannot tell from your payslip. Arrears of overtime and public holiday pay are not always pensionable; the Grey Book says public holiday double time is not pensionable.

If a lump-sum arrears payment pushes you into a higher rate band for that month, the tax adjusts across the year and can be reconciled at the end of the tax year. The take-home pay guide explains the deductions, and the tax code guide explains codes.

How to check arrears on your payslip

Work through the following steps when your payslip arrives after an award. Have the NJC circular, your contract and your last two payslips to hand, and note the pay dates. If you are paid four-weekly, keep track of which pay periods fall before and after 1 July, because a period that straddles the date may be split.

1. Find your role and stage on your payslip or contract, and the correct annual rates in the NJC circular for the old and new year.
2. Check that your new basic pay per period equals annual ÷ 12 (or ÷ 13 for four-weekly), and that the new rate applies from the payslip your service said it would implement.
3. Look for a separate arrears or back-pay line. It may be labelled arrears, backdated pay, pay award adjustment or something similar. If it is absent, ask whether it is included in another line.
4. Calculate the expected arrears from the annual difference and the number of periods paid at the old rate, then compare. Allow a few pence for rounding.
5. Check the overtime, on-call activity, retainer and CPD lines too, and confirm each moved by 3.8% from 1 July 2026 or has its own arrears amount.
6. Note the tax and National Insurance taken on the arrears line, and keep a copy of every payslip and your service's implementation notice.

A larger backdated award: the 2022 example

The 2022 award shows how much larger arrears can be when confirmation is late. The 7% increase took effect on 1 July 2022, taking a competent firefighter from £32,244 to £34,501, an annual difference of £2,257, or £188.08 a month. The circular confirming it is dated 6 March 2023, eight months after the effective date. If payroll had paid all eight months of the difference in one go, a competent firefighter's basic pay arrears would have been 8 × £188.08 = £1,504.67 gross, before overtime, CPD and on-call elements.

That is an illustration of the arithmetic, not a record of what any particular service paid or when. London Fire Brigade's FOI response of 11 September 2023 says its policy shows implementation dates in an implementation section and describes the 2023 rates being paid in July 2023 salaries. The timing for other services and for the 2022 arrears varied and is not stated in the sources reviewed for this guide.

The lesson is practical: if a service is slow to implement an award, the amount owed grows each month, which is why it is worth checking early and asking for a date. See firefighter pay rises history for the timing of each award.

If your arrears are missing or wrong

Start with payroll or HR. Ask in writing for the implementation date, the calculation of arrears, and the pay period in which they will be paid, quoting the NJC circular reference (NJC/2/26 for 2026). Give your role, stage and the figures you calculated. Most differences are timing or rounding, and a written question usually resolves them quickly.

If you are an FBU member, your local representative can raise it with the service, and the union has urged employers to apply awards to all Grey Book employees as a matter of urgency. If the issue is not resolved, your service's grievance procedure is the formal route. Keep a record of dates and responses. This guide is not legal advice; for employment-law questions, Acas is an independent source of guidance.

Employees who have left the service, retired or moved between services since 1 July may still be owed arrears for the period they were employed, and pension benefits may need recalculating. Ask your former service and your pension administrator how they handle this, since it depends on local processes and scheme rules.

Planning for arrears

Arrears can be a useful lump sum, but treat them with care. Tax on a lump sum can make the payslip look smaller than expected, and the net amount will be below the gross figures in this guide. A gross £369.25 arrears payment for a competent firefighter is roughly £266 after 20% tax and 8% National Insurance if it is all taxed at basic rate (£369.25 × 0.72 = £265.86), before any pension contribution on the pensionable element.

If you are budgeting or applying for credit, use your new monthly pay, not a month that includes arrears, as your baseline. The pay calculator shows net pay at the new rates, and the overtime to deposit tool is one way to plan a lump sum toward a goal.

For a personal written summary of your pay position, including what arrears you should expect, the paid Personal Pay Report is designed for exactly this kind of check. For the wider context of how awards are made, see the FBU pay claim and NJC process and firefighter pay scales 2025 vs 2026.