To get emergency tax back from HMRC, you need to give them the information that was missing when your employer first put you on the emergency code. Once HMRC has it, they issue a correct cumulative tax code and the overpayment comes back to you, either through your payslip during the tax year or as a P800 refund after it ends. The fastest way to trigger that is through your Personal Tax Account on GOV.UK, or by handing your new employer a P45 from your last job.
Check That You’re Actually on an Emergency Code
Look at your most recent payslip. If your tax code ends in W1, M1, or X, you’re on an emergency code. Some payroll systems show “NONCUM” instead.1GOV.UK. Tax Codes: Emergency Tax Codes
The reason this costs you money is that an emergency code treats each pay period on its own, ignoring what you’ve earned earlier in the tax year. If you had months of unused personal allowance before starting the job, an emergency code won’t recognise it, and the tax deduction is higher than it should be. That gap is your overpayment, and it grows with every payslip until the code is corrected.
These codes usually appear when you start a new job without a P45, move from self-employment onto a payroll, or start your first job with no earnings history.2GOV.UK. Understanding Your Employees’ Tax Codes
Get the Right Paperwork to Your Employer
The single quickest fix is a P45 from your previous job. It shows your pay and tax so far in the tax year, which gives HMRC everything needed to work out the correct code.3GOV.UK. Tax Codes: How to Update Your Tax Code If you left a job and never received one, ask your former employer for it directly.
No P45? Your new employer should give you a Starter Checklist, which replaced the old P46. It asks whether you have another job, receive a pension, or have a student loan, and your employer uses those answers to set your initial code and register you with HMRC.4GOV.UK. Starter Checklist for PAYE Answer it carefully. Ticking the wrong box about having another job can land you on a more restrictive code than the one you started with.
Have your National Insurance number to hand as well. It’s how HMRC links your records together. Your employer’s PAYE reference, printed on your payslip, is worth noting too if you plan to contact HMRC yourself.
Update Your Tax Code Through HMRC
Sign in to your Personal Tax Account on GOV.UK and use the “Check your Income Tax” service. You can see your current code, the income HMRC has recorded from jobs and pensions, and correct anything that’s wrong or missing.5GOV.UK. Check Your Income Tax for the Current Year The HMRC app does the same job from a phone.
Once you’ve updated your details, HMRC reviews them and, if the code needs changing, tells both you and your employer within 15 working days. The corrected code should show on your next monthly payslip, or within three payslips if you’re paid weekly.3GOV.UK. Tax Codes: How to Update Your Tax Code
If you’ve just started a new job, HMRC asks you to wait 35 days before contacting them. Payroll data takes that long to reach their systems, and calling sooner won’t speed anything up.3GOV.UK. Tax Codes: How to Update Your Tax Code
If the online service isn’t working for your situation, call HMRC’s Income Tax helpline on 0300 200 3300, Monday to Friday, 8am to 6pm.6GOV.UK. Income Tax: Enquiries Have your National Insurance number and employer details ready.
One boundary worth flagging: if you pay income tax only through Self Assessment, this online service isn’t for you. Any overpaid tax is sorted through your Self Assessment return.5GOV.UK. Check Your Income Tax for the Current Year
How the Refund Reaches You
Through Your Payslip During the Tax Year
If HMRC corrects the code before 5 April, the refund comes through your wages. Your employer applies the new cumulative code, recalculates the tax you’ve paid for the year so far, and the difference lands as a reduced deduction on your next payslip. It can look startling, sometimes the net figure is much bigger than usual, but it’s the system returning what it overcharged in earlier months.
This is the outcome you want, and it’s the main reason to act early. Leave it until March and the tax year may close before the adjustment can be made through payroll.
By P800 After the Tax Year Ends
If the tax year finishes first, HMRC sends a P800 tax calculation letter. It compares what you earned against what you paid and states the refund amount.7GOV.UK. Tax Overpayments and Underpayments P800s usually arrive between June and October after the tax year in question.
If the letter tells you to claim online, log into your Personal Tax Account and request the money there. Online claims arrive within five working days. Ask for a cheque instead and it takes up to six weeks.8GOV.UK. Tax Overpayments and Underpayments: If You’re Due a Refund
Some P800s say a cheque will be sent automatically without you having to claim. In that case, it should reach you within 14 days of the date on the letter.8GOV.UK. Tax Overpayments and Underpayments: If You’re Due a Refund The overpayment sits on your record until it’s repaid, even if you’ve since changed jobs or stopped working.
The Four-Year Deadline
You have four years from the end of the tax year in which you overpaid to claim the money back. Miss that window and the refund is lost. Overpaid during 2025/26, which ends 5 April 2026? Your deadline is 5 April 2030.
If HMRC doesn’t pick up the overpayment automatically through a P800 and you never check, four years passes quickly. For a previous tax year still inside the window, use the “Claim a tax refund” tool on GOV.UK or write to HMRC to ask them to review it.