What is back pay? UK guide for employers and payroll

Published Friday 17 April 2026

Table of contents

• What is back pay?
• How does back pay work in the UK?
• Examples of back pay
• Are employers required to pay back pay?
• How to calculate back pay
• How to issue back pay to employees
• How to ensure back pay is included when running payroll
• Managing back pay with confidence
• FAQs on back pay

Key takeaways

• Recognize that back pay is a legal obligation — if you underpay an employee, whether by accident or not, you must pay the full amount owed, or risk penalties of up to £20,000 per worker and potential legal action.
• Act quickly when you discover an underpayment, as paying all unpaid wages in full within 14 days can reduce any related penalty by 50%.
• Calculate back pay based on employment type — multiply unpaid hours by the hourly rate for hourly workers, or divide the annual salary by working days in the year to find the daily rate for salaried employees.
• Use automated payroll software to catch errors before they happen, keeping accurate records and reducing the risk of underpayments in the first place.

What is back pay?

Understanding back pay is essential for employers. Back pay is the difference between what you pay an employee and what they should have been paid. It's the money you owe when someone has been underpaid for work they've already done.

Underpayments can happen for all kinds of reasons: administrative errors in payroll, overtime that hasn't been tracked, or delayed processing of a pay rise.

If you've accidentally underpaid someone, get it sorted as soon as possible. Any related penalty is reduced by 50% if you pay all unpaid wages in full within 14 days. Managing back pay properly keeps your team happy and your finances on track.

How does back pay work in the UK?

Here's how the back pay process typically works. Back pay works by correcting past underpayments through your payroll system. When you underpay an employee, they can raise a claim with whoever handles your pay, whether that's an outsourced provider, accountant, or internal finance team.

You then verify the claim against timesheets and records, calculate the amount owed, and process the payment. Checking payments carefully before each pay run helps you avoid these situations.

Examples of back pay

Back pay situations happen regularly in businesses of all sizes. Here are the most frequent triggers:

• Delayed pay rises: an employee's increase was approved but you didn't process it in time for the latest pay run
• Payroll errors: entering a missed digit, mistyped name, or incorrect hours on a timesheet
• Unrecorded overtime: extra hours the employee worked but didn't capture or communicate to payroll
• Minimum wage shortfalls: rates increased but you didn't update your payroll system, meaning employees received less than the legal minimum

When you use automated payroll software, mistakes like these are far easier to prevent.

For guidance on tax deductions for back pay, check HMRC's PAYE manual or speak with a payroll professional.

Are employers required to pay back pay?

The short answer is clear. Yes, employers are legally required to pay back pay. If you've underpaid an employee, whether accidentally or not, you must pay them the full amount owed.

Failing to pay has serious consequences:

• Breach of contract: your employees can take legal action to recover unpaid wages
• HMRC penalties: not complying with pay laws can result in fines or even a custodial sentence of up to two years for key labour market offences
• Minimum wage enforcement: under the Employment Rights Act 1996, failing to pay minimum wage can lead to significant financial penalties, where the maximum penalty is £20,000 per worker

How to calculate back pay

There are different ways to calculate back pay depending on whether your employees are hourly or salaried. Let's look at calculations for both.

Hourly employees

For hourly employees, calculate back pay by multiplying the unpaid hours by their hourly rate. If overtime applies, use the overtime rate for those hours.

Example: Your employee Callum is paid £9 per hour. He was paid for 30 hours last week, but his timesheets show he worked 35. The extra five hours should be paid at his overtime rate of £10 per hour.

• Hours paid: 30 x £9 = £270
• Overtime owed: 5 x £10 = £50

Back pay due: £50

Salaried employees

For salaried employees, you'll need to calculate their daily or hourly rate first, then multiply by the unpaid time.

Example: Your employee Jasmine earns £45,000 per year. She worked an extra day last month that wasn't included in her pay. Her contract states overtime is calculated based on her annual salary.

• Working days per year: 260
• Daily rate: £45,000 ÷ 260 = £173.08
• Extra days worked: 1

Back pay due: £173.08

How to issue back pay to employees

Once you've confirmed an employee is owed back pay, process it through your normal payroll system. Here's how:

1. Verify the claim: check their hours against timesheets, contracts, or other records you keep
2. Calculate the amount: work out exactly what's owed using the methods above
3. Agree a timeline: if cash flow is tight, discuss a payment schedule with your employee
4. Process the payment: run the back pay through your payroll system
5. Update your records: ensure your payroll records reflect the correction

Be transparent with your employee throughout. Reassure them they'll receive what they're owed based on their contract.

How to ensure back pay is included when running payroll

Prevention is better than correction. Automated payroll systems reduce back pay situations by catching errors before they happen. When your payroll runs smoothly, you spend less time on corrections and more time on your business.

Xero payroll software helps you stay on top of employee payments:

• Custom pay rates: set different rates for regular hours, overtime, and other pay types
• Accurate records: keep payroll data stored securely in the cloud
• HMRC compliance: send compliant reports directly to HMRC

For more help with online payroll for small businesses, check out the other guides on Xero, or explore the free Basic PAYE Tools software provided by HMRC for businesses with fewer than 10 employees.

Managing back pay with confidence

Getting back pay right protects your business and maintains trust with your team. The key steps are straightforward: identify the underpayment, calculate what's owed, and process it through your payroll system promptly.

With the right tools, you can prevent most back pay situations. Automated payroll software catches errors early, keeps accurate records, and ensures you pay your employees correctly every time.

Ready to simplify your payroll? Get one month free and see how Xero can help you stay on top of employee payments.

FAQs on back pay

Here are answers to common questions employers have about back pay.

How far back can employees claim back pay?

In the UK, employees can typically claim unpaid wages going back six years. For minimum wage claims, HMRC can investigate records from the previous six years.

What if I can't afford to pay back pay immediately?

Speak with your employee and agree a payment plan. Document the arrangement in writing, including the total amount owed and the payment schedule.

Does back pay affect PAYE and National Insurance calculations?

Yes. You deduct the same tax and National Insurance from back pay as you do from regular pay. Process it through your payroll system to ensure you make the correct deductions.

Do I need to pay back pay if an employee has already left?

Yes. You still owe former employees any wages they earned while working for you. You'll need to process the payment and provide an updated P45 if necessary.

What records should I keep when paying back pay?

Keep a record of what you originally underpaid, how you calculated the back pay amount, when you made the payment, and any messages you exchanged with the employee about the issue.