NHS Back Pay Calculator
Estimate retrospective pay owed for an NHS pay rise, a promotion, or an acting-up period — gross and after tax, NI & pension.
Your Details
New-salary helper (2026/27 AfC)
Arrears Period
Monthly Difference
Deduction Breakdown
How NHS Back Pay Works
NHS back pay is the difference between what you should have been paid and what you were actually paid for a period of work. It is owed in three common situations and is paid as a single lump sum, after Income Tax, National Insurance and pension contributions are deducted at source.
Pay Rise / Annual Award
Each AfC pay deal is usually announced months after April and applied retrospectively. The arrears for April through the month payroll catches up land in a single lump-sum back pay payment.
Promotion or Re-banding
When a band uplift, job-evaluation upgrade, or contract change is approved with an effective date earlier than payroll processed it, you are entitled to the salary differential for the period in between.
Acting Up / Higher Duties
If you covered a higher-banded role and the Acting Up payment was processed late, your employer owes you the salary differential between your substantive band and the higher band for the period worked.
How the Calculation Works
Gross back pay
- Daily difference: (new annual − old annual) ÷ 365.25
- Pro-rated for part-time hours (hours ÷ 37.5)
- Multiplied by the number of days in the arrears period
- HCAS / London weighting applied to both salaries before the difference is taken
Estimated deductions
- Income Tax at your marginal rate (20% / 40% / 45%)
- NI Class 1 at 8% (or 2% above £50,270/yr)
- NHS Pension at the tier matching your new annual salary (5.2%–12.5%)
- Lump-sum arrears can briefly push you into a higher tax bracket the month they're paid
What is the NHS Back Pay Calculator?
The NHS Back Pay Calculator is an online tool that helps NHS employees estimate the arrears they are owed when their pay has changed retrospectively. It supports the three most common back-pay situations — an annual pay award, a promotion or re-banding, and an acting-up assignment — and produces both a gross figure and an estimated net figure after Income Tax, National Insurance and NHS Pension contributions. The calculator works for staff on Agenda for Change Bands 2 to 9, in any UK NHS region, and accounts for part-time hours and London / HCAS weighting where applicable.
What is NHS back pay?
NHS back pay is the difference between the salary you should have been paid and the salary you were actually paid for a defined period of work. It is most commonly owed when a national pay deal is agreed retrospectively, when a promotion or re-banding has an effective date earlier than the date payroll caught up, or when an acting-up payment for covering a higher-banded role is processed late.
Who is eligible for back pay?
Eligibility depends on the scenario, but in most cases:
- Pay award arrears: All staff employed under Agenda for Change during the effective period of the new pay deal automatically qualify.
- Promotion arrears: Staff whose new band has been formally approved with an effective date earlier than payroll implemented it.
- Acting-up arrears: Staff who covered the full duties of a higher-banded role with manager approval, typically for a continuous period of four weeks or more.
How is NHS back pay calculated?
The gross back pay is calculated by taking the difference between the new annual salary and the old annual salary, dividing by 365.25 to get the daily difference, multiplying by the number of days in the arrears period, and pro-rating for part-time hours where applicable. London / HCAS weighting is applied to both salaries before the difference is taken, so the differential is not double-counted. Income Tax, National Insurance and NHS Pension contributions are then deducted at the rates that apply to your new annual salary.
Why is the tax on my back pay so high?
Back pay is paid as a single lump sum, so it lands in one tax month on top of your normal salary. PAYE briefly treats your monthly earnings as if they were your new annual rate, which can push some of the lump sum into the higher 40% tax bracket and reduce NI to 2%. Over the full tax year, HMRC reconciles this so you only ever pay tax based on your true annual income — any short-term over-deduction is refunded automatically through your subsequent payslips.
When will I receive my NHS back pay?
For an annual pay award, back pay is normally paid in the first or second pay packet after the deal is formally accepted — typically two to three months after the effective April date. For promotions and acting-up payments, the timing depends on when payroll receives the authorisation paperwork from your line manager.
Does back pay count towards my NHS Pension?
Yes. NHS back pay is pensionable earnings and pension contributions are deducted from the gross figure at the tier matching your new annual salary. The arrears are credited to your pensionable earnings record for the year in which they relate, not the year they are paid, which can affect your final-salary or career-average calculation.
Is acting-up back pay automatic?
No. Acting-up payments require formal manager approval and a payroll change form. If you have been covering a higher-banded role without the corresponding pay, you should raise it with your line manager and HR — back pay can usually be claimed for the full period the duties were carried out, subject to your trust's policy.
How does back pay differ for part-time staff?
Part-time NHS staff receive back pay pro-rated to their contracted hours. The calculator divides your contracted weekly hours by 37.5 (the standard full-time equivalent) and multiplies the differential by that factor. Bank, agency and zero-hours workers are typically not covered by AfC pay arrears and are paid on a different model.
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