Emergency Tax Code UK 2026/27: Why You're Overpaying and How to Get Your Money Back

By the UK Salary Take Home Editorial Team · Published 24 Mar 2026

If your payslip shows a tax code ending in W1, M1, or X — or simply says BR or 0T — you're on an emergency tax code. This means HMRC hasn't confirmed your tax allowances to your employer, so payroll is using a worst-case default to avoid undertaxing you. The result: you overpay, sometimes by hundreds of pounds per month.

HMRC processed over 2.8 million emergency tax corrections in the 2024/25 tax year. This guide explains exactly what's happening, how much extra you're losing, and the fastest way to fix it.

1. What Is an Emergency Tax Code?

An emergency tax code is a temporary code HMRC instructs your employer to use when they don't have enough information to calculate your tax correctly. Instead of risking an underpayment, they err on the side of overtaxing you.

The three most common emergency codes in 2026/27 are:

The suffix W1 (Week 1) applies to weekly-paid employees; M1 (Month 1) to monthly-paid employees — both mean the same thing: non-cumulative calculation. Some payslips show X instead.

2. What Triggers an Emergency Tax Code?

Five common scenarios:

1. New job, no P45: Your previous employer was slow to issue your P45, or you didn't pass it to your new employer. Without it, payroll has no record of your year-to-date earnings or tax paid.
2. First job ever: If you've never been in PAYE before (e.g., a graduate starting work), HMRC has no record of you. Your employer starts you on an emergency code until HMRC confirms your allowances.
3. New starter declaration incomplete: Your employer should give you a “Starter Checklist” (replaced the P46). If you choose Statement B or C instead of A (“This is my first job since 6 April”), payroll may assign an emergency code or BR.
4. Company benefits not yet processed: If you have a company car or medical insurance and HMRC hasn't updated your coding notice (P2) yet, they may issue 0T temporarily.
5. Returning from abroad: If you've been working overseas and re-enter the UK PAYE system mid-year, HMRC may not have your tax residence status confirmed.

3. How Much Extra Are You Paying? — Worked Examples

Let's quantify the damage for a £30,000 salary (standard case: tax code 1257L, no pension):

Scenario A: Correct Code (1257L cumulative)

Scenario B: Emergency Code (1257L M1)

Scenario C: Emergency Code (BR)

Scenario D: Emergency Code (0T)

At £55,000, the damage from 0T is much worse: you lose both the £12,570 allowance and get pushed into the Higher Rate band sooner. Monthly overpayment on 0T at that salary exceeds £400/month.

4. How to Fix It — Step by Step

Speed matters. Every pay cycle on a wrong code is money trapped with HMRC until the correction flows through. Here's the fastest path:

1. Give your P45 to your employer immediately. If you have a P45 from your previous job, hand it over on your first day. This single document contains your year-to-date earnings and tax paid, allowing payroll to calculate correctly from day one.
2. Complete the Starter Checklist correctly. If you don't have a P45, your employer gives you this form. Choose Statement A if this is your only or main job since 6 April. Statement B means you have another job but want this to use your full allowance. Statement C means you have another job and want BR applied (no allowance).
3. Check your code on HMRC Personal Tax Account. Sign in at gov.uk/personal-tax-account. Under “Check your Income Tax”, you'll see your current code and can request a change if it's wrong. Changes made here typically reach your employer within 2 weeks.
4. Call HMRC if it's urgent. Phone 0300 200 3300 (Monday–Friday, 8am–6pm). Have your NI number, employer's PAYE reference (on your payslip), and details of your previous employment. HMRC can issue an updated code by phone the same day.
5. Wait for the automatic refund. Once your employer receives the corrected cumulative code, their payroll software recalculates your year-to-date tax. If you've overpaid, the difference is refunded in your next pay packet — often as a noticeably larger payment.

5. What If the Tax Year Has Already Ended?

If you were on emergency tax for part of a tax year that has now ended and the overpayment wasn't corrected through payroll, HMRC will usually send you a P800 tax calculation after July. This letter shows whether you overpaid or underpaid.

If you're owed a refund:

• You can claim online via your Personal Tax Account for a faster bank transfer (typically within 5 working days)
• If you don't claim online, HMRC posts a cheque within 60 days of the P800 being issued
• If you don't receive a P800 and believe you overpaid, you can write to HMRC or use form R40 (repayment claim)

You have 4 years from the end of the tax year to claim overpaid tax. After that, the right to reclaim expires.

6. Emergency Tax and Your First UK Job

Graduates and first-time workers are most affected because they often don't know what to expect on a payslip. If you started your first-ever job in September (Month 6), you're entitled to 6 months of back-dated Personal Allowance that an emergency code won't give you.

On a starting salary of £28,000:

The fix is the same: ensure the Starter Checklist is completed with Statement A, then check your HMRC Personal Tax Account after 4–6 weeks. If the code still shows M1, call HMRC.

7. How to Spot Emergency Tax on Your Payslip

Emergency codes don't always scream “EMERGENCY.” Here's what to look for:

• Tax code field shows W1, M1, or X after the number (e.g., 1257L M1)
• Tax code shows BR when this is your only job
• Tax code shows 0T (zero allowance)
• Year-to-date tax figure is significantly higher than what our salary calculator shows for the same period
• Your tax deduction jumps noticeably in the first month at a new job compared to your last payslip from your previous employer

For a full guide to every tax code variation and what the letters mean, see our Understanding Your Tax Code article.

8. Preventing Emergency Tax in Future Job Changes

Three habits that prevent the problem entirely:

1. Ask for your P45 on your last day. Employers have a legal obligation to provide a P45 when you leave. If it's not ready on your final day, follow up within a week. Keep a digital copy.
2. Hand the P45 to your new employer before your first payday. If you start on 1 June but your first pay run is 28 June, you have nearly a month — but don't wait. Give it on day one.
3. Register for the HMRC App. The app shows your current tax code in real time and sends push notifications when your code changes. You can spot and fix errors before they hit your payslip.