0T WK1 Tax Code: Meaning, Pay Impact, and How to Fix It

A 0T W1 tax code means your employer is deducting income tax from every pound you earn, giving you no Personal Allowance, and treating each pay period on its own rather than looking at what you’ve already earned or paid this tax year. The “0T” strips out the £12,570 tax-free threshold. The “W1” (or “M1” if you’re paid monthly) switches off the cumulative calculation that would normally smooth out over- and under-payments across the year. For most people, this combination results in paying more tax than they actually owe. Once HMRC has the right information, the code changes and any overpayment comes back to you.

What Each Part of the Code Does

A PAYE tax code has a number and a letter. The number is your annual tax-free income divided by ten, so 1257L means £12,570 tax-free. A code starting with 0 means your tax-free amount is zero, and every pound gets taxed from the first penny.¹

The W1 or M1 suffix tells payroll software to work non-cumulatively. Under a normal cumulative code, the software tracks everything you’ve earned and taxed since 6 April, so if you overpay one month it corrects itself the next. Under W1/M1, each pay period is treated as though it were the very first of the tax year. Nothing carries forward.² Your payslip may show “NONCUM” or “X” instead of W1 or M1, depending on the software.³

HMRC’s stated purpose for the non-cumulative basis is to “prevent the employer making heavy deductions or giving any refund.”² Combined with the zero allowance in 0T, the effect is that you’re taxed on your full earnings every pay period with no built-in mechanism to correct itself.

Why You’re on It

The most common trigger is starting a new job without giving your new employer a P45 from your previous one. Without the P45, the employer has no record of your prior earnings or tax paid, so payroll defaults to 0T on a non-cumulative basis to avoid a large underpayment surfacing later.³

Other common reasons:

You have a second job or a pension alongside employment. Your Personal Allowance is already applied to the main income, so the second source gets a code without any allowance.⁴
Your income is above £100,000. You lose £1 of Personal Allowance for every £2 over that threshold, and at £125,140 or above your allowance is zero.⁵
Your Starter Checklist wasn’t completed or the information was incomplete. Where a new starter has no P45, this form is the backup HMRC and the employer rely on. Without it, 0T is the default.⁶

For high earners whose Personal Allowance is genuinely tapered to nil, 0T is the correct permanent code. For everyone else it’s a placeholder that gets replaced once HMRC has your employment details.

What It Does to Your Pay

Because your Personal Allowance is zero, your entire earnings hit the tax bands from the first pound. For the 2025/26 tax year (6 April 2025 to 5 April 2026), the rest-of-UK bands are:⁵

Basic rate of 20% on taxable income up to £37,700
Higher rate of 40% from £37,701 to £125,140
Additional rate of 45% above £125,140

Under a normal code, the first £12,570 of income would be tax-free and the bands would sit above that. Under 0T the bands still apply at their usual widths, but they kick in immediately. Earn £1,000 in a week and the whole amount falls inside the basic rate band, so £200 is deducted. Earn £4,000 in a week and roughly the first £3,142 is taxed at 20% (the weekly slice of the £37,700 band) with the rest at 40%.

The non-cumulative element makes things worse in practice. If you started a job partway through the tax year, a cumulative code would use your unused allowance from earlier months to reduce the current deduction. W1 doesn’t know those earlier months exist. Every pay period stands alone.

Pension Withdrawals

Pension providers frequently apply 0T or 1257L on a Month 1 basis when processing lump-sum or ad-hoc withdrawals. This catches many people off guard. The provider treats a single withdrawal as though you’ll receive that amount every month for the rest of the year, which can push a modest withdrawal into the higher or additional rate band.

Take £30,000 out in one go and it can be taxed as if your annual income were £360,000, with a large chunk falling into the 40% and 45% bands. In reality it may be your only withdrawal that year, and the overtaxation on a single payment can run to thousands of pounds.

You don’t have to wait until the end of the tax year to reclaim it. HMRC has dedicated forms: P53 if you’ve taken a small pension lump sum, and P53Z if you’ve flexibly accessed and emptied a pot.⁷ For regular pension payments, HMRC will eventually issue an updated code to the provider that corrects things going forward.

Scottish Taxpayers

If you live in Scotland, your code should carry an “S” prefix, so S0T W1 rather than 0T W1, and your income is taxed at Scottish rates. The 2025/26 Scottish bands are:⁸

Starter rate 19% on £12,571 to £15,397
Basic rate 20% on £15,398 to £27,491
Intermediate rate 21% on £27,492 to £43,662
Higher rate 42% on £43,663 to £75,000
Advanced rate 45% on £75,001 to £125,140
Top rate 48% above £125,140

Under S0T those bands apply from the first pound with no Personal Allowance. The top rate of 48% is three points higher than the rest-of-UK additional rate, so a Scottish 0T code can bite harder. If your code shows plain 0T without the S prefix and you live in Scotland, that’s a second problem worth flagging.

How 0T Compares to BR and 1257L W1/M1

Several codes can turn up on a payslip when HMRC lacks full information, and the differences matter for take-home pay:

1257L W1/M1 is the standard emergency code for 2025/26. You still get a proportional Personal Allowance each period (£242 a week or £1,048 a month), just on a non-cumulative basis. This is the mildest version.
BR taxes all income from that source at a flat 20% with no Personal Allowance, and is typically used for a second job or pension where the allowance is applied elsewhere.¹
0T W1/M1 is the harshest. No Personal Allowance, and progressive rates up to 45%, applied afresh each pay period.

Someone earning £50,000 a year on BR pays a flat 20% on everything from that source. The same person on 0T pays 20% on most of their income but 40% on the slice above the weekly equivalent of the £37,700 band. BR is predictable but can also overtax you if your allowance should have been applied to that job. 0T is almost always worse for anyone earning above the basic rate threshold.

Getting the Code Corrected

If 0T W1 is wrong for your situation, fixing it needs you to act rather than wait. Start with the Check your Income Tax online service through your Personal Tax Account on GOV.UK. You can review the employment, pension, and income details HMRC currently holds and update anything missing or wrong.⁹

If you’ve just started a new job, HMRC advises waiting 35 days for your employer’s payroll data to reach their systems before contacting them.⁹ The fastest fix, if you can manage it, is giving your employer a P45 from your previous job. If you don’t have one, complete the Starter Checklist so your employer can submit the right information with their next Full Payment Submission.⁶

If the online service doesn’t resolve it, contact HMRC’s Income Tax helpline. Once HMRC updates your records they send a P2 coding notice (by post or in your Personal Tax Account) and notify your employer electronically.¹⁰ Your employer then applies the new code to the next available payroll run.

Getting Overpaid Tax Back

Most people on 0T W1 overpay, and there are two ways the money comes back.

The fastest is getting the code corrected mid-year and switched to a cumulative basis. Once payroll has the right cumulative code, it recalculates your tax from the start of the tax year. Any overpayment shows up as a larger-than-normal net pay in the next pay run or two, until things are square. No forms, no waiting.

If the tax year ends before the code is fixed, HMRC reconciles your account after 5 April and sends a P800 tax calculation, typically between June and November. The P800 shows what you owed versus what you paid. If you’re due a refund and the letter says you can claim online, the money arrives within five working days of the claim. If HMRC sends the refund automatically by cheque, it comes within 14 days of the letter date.¹¹

If no P800 arrives and you think you’ve overpaid, use the Check how to claim a tax refund tool on GOV.UK.¹² The deadline for reclaiming overpaid tax is four years from the end of the tax year in which the overpayment occurred. For 2025/26 overpayments, that means 5 April 2030. After the window closes, the money is gone.

1
GOV.UK. Tax Codes – What Your Tax Code Means
2
GOV.UK. PAYE Manual – Coding: Codes: How They Are Used and Calculated: Ways an Employer Can Operate a Code
3
GOV.UK. Tax Codes – Emergency Tax Codes
4
GOV.UK. Understanding Your Employees’ Tax Codes: What the Letters Mean
5
GOV.UK. Income Tax Rates and Personal Allowances
6
GOV.UK. Starter Checklist if You’re Starting a New Job
7
GOV.UK. Claim a Tax Refund When You’ve Taken a Small Pension Lump Sum (P53)
8
GOV.UK. Income Tax in Scotland: Current Rates
9
GOV.UK. Tax Codes – If You Think Your Tax Code Is Wrong
10
GOV.UK. PAYE Manual – Coding: Codes: How They Are Used and Calculated: P2 Notice of Coding
11
GOV.UK. If Your Tax Calculation Letter (P800) Says You’re Due a Refund
12
GOV.UK. Check How to Claim a Tax Refund