0T W1 Tax Code: What It Means, Why It’s Applied, and How to Fix It

The 0T W1 tax code is an emergency PAYE code that strips out your Personal Allowance and taxes each pay period in isolation, so you pay income tax from the very first pound of that payslip and nothing carries over from earlier in the year. You’ll usually see it after starting a new job without a P45, and it stays in place until HMRC has enough information to issue your correct code.¹

What the Code Actually Means

The code splits into two parts. “0T” tells your employer that no Personal Allowance applies to your pay from that job. The standard code 1257L would normally give you £12,570 of tax-free income spread across the year; with 0T, that allowance drops to zero.¹

“W1” stands for Week 1 and signals a non-cumulative calculation. Payroll ignores everything you earned or paid in tax earlier in the year and treats each pay period as though it were the first.² If you’re paid monthly, the same code appears as 0T M1. The effect is identical.

Your pay is then run through the standard income tax bands for England, Wales, and Northern Ireland:

Basic rate of 20% on earnings up to £50,270
Higher rate of 40% on earnings from £50,271 to £125,140
Additional rate of 45% on earnings above £125,140

Because no tax-free slice is applied first, the 20% rate bites from the very first pound.³ Scottish taxpayers see an “S0T W1” instead, with a different set of rates.⁴

Why HMRC Has Assigned It to You

HMRC uses 0T W1 as a safety net when it doesn’t have enough data to work out your correct position. A few situations trigger it:

You started a new job without handing over a P45. Your employer has no record of your earlier earnings or tax paid that year, and the fallback under the starter checklist process is 0T on a non-cumulative basis.⁵
You ticked Statement C on the starter checklist (“As well as my new job, I have another job or receive a State or Occupational Pension”), or you didn’t complete the checklist at all.⁶
This is a second job and your main employer is already using your full Personal Allowance through 1257L. There’s no allowance left to give the second job, so HMRC assigns 0T (or sometimes BR) to it.

One boundary is worth flagging. Your Personal Allowance tapers by £1 for every £2 of adjusted net income over £100,000, and it reaches zero at £125,140. Above that figure, 0T is your correct permanent code, not an emergency one.³ The clue is the suffix: if W1 or M1 sits alongside the 0T, HMRC is still working things out. If the code reads simply “0T” with no suffix, it may be right.

What Non-Cumulative Actually Does to Your Pay

A normal cumulative code like 1257L tracks your total earnings from 6 April onwards. Each pay period, payroll compares what you’ve earned so far against the tax-free amount you should have received by that point, smoothing things out across the year.⁷

The W1 or M1 suffix breaks that link. Payroll looks only at the current pay period and taxes it as though you’ll earn the same amount every week or month for the rest of the year. Previous overpayments don’t offset the current period, and unused allowance from months when you weren’t working doesn’t accumulate.²

Say you earn £3,000 in a particular month. Under 1257L on a cumulative basis, roughly £1,048 of that would be sheltered by your monthly slice of the Personal Allowance. Under 0T M1, the whole £3,000 is taxable, and the system assumes you’ll earn £3,000 every month for the year. The deduction is visibly bigger, sometimes by hundreds of pounds.

How to Get the Code Corrected

HMRC will often fix the code automatically once your employer submits payroll data, but that can take a few weeks. If it lingers past your first full pay period, act rather than wait.

The fastest route is your Personal Tax Account on GOV.UK. Sign in, go to the income tax section, and check what HMRC holds about your earnings and tax code. You can update missing details, such as a new employer or pension, directly through the online service.⁸ The HMRC app does the same job on a phone.⁹

Have these to hand before you start:

Your National Insurance number. If you’ve lost it, the GOV.UK “Find your National Insurance number” service retrieves it online.¹⁰
Your employer PAYE reference, which appears on your payslip.
An estimate of your total annual income from all jobs, pensions, and other taxable sources, so HMRC can set the right band.

If you can’t use the online service, call the income tax helpline on 0300 200 3300 (Monday to Friday, 8am to 6pm).¹¹ Once HMRC processes the update, they notify your employer of the revised code and your next payslip should reflect it.¹²

Getting Back the Tax You’ve Overpaid

When your code is corrected to a cumulative one mid-year, your employer’s payroll recalculates your tax position from 6 April and adjusts your next pay to account for the earlier overpayment. In many cases the refund arrives through your wages without a separate claim.

If the tax year has already ended before the correction goes through, HMRC reviews PAYE records and issues a P800 tax calculation letter. These are sent between June and March of the following tax year.¹³ The P800 tells you the amount overpaid and lets you claim online, with the money usually reaching your bank account within five working days of the claim.

If you think you’ve overpaid but no P800 has arrived, GOV.UK’s “Check how to claim a tax refund” tool routes you to the right form for your situation.¹⁴

Being on 0T W1 doesn’t by itself require you to file a Self Assessment tax return. Most employees resolve everything through the Personal Tax Account or the helpline. Self Assessment only comes in if you meet the normal criteria for it, such as self-employment income or total earnings above £150,000.⁷

1
GOV.UK. Tax Codes: What Your Tax Code Means
2
GOV.UK. PAYE Manual PAYE11090
3
GOV.UK. Income Tax Rates and Personal Allowances
4
GOV.UK. Income Tax in Scotland
5
GOV.UK. Tell HMRC About a New Employee
6
GOV.UK. Employer Help Card: Understanding the Starter Declaration Form
7
GOV.UK. Tax Codes – Section: Emergency Tax Codes
8
GOV.UK. Check Your Income Tax for the Current Year
9
GOV.UK. Personal Tax Account: Sign In or Set Up
10
GOV.UK. Find Your National Insurance Number
11
GOV.UK. Income Tax: Enquiries
12
GOV.UK. Tax Codes
13
GOV.UK. Tax Overpayments and Underpayments
14
GOV.UK. Check How to Claim a Tax Refund