0T W1 Tax Code Explained: What You Need to Know?

Last Updated on: 24th July 2025, 11:32 am

Have you recently noticed the 0T W1 tax code on your payslip and wondered what it means? You’re not alone. Many UK taxpayers encounter this unfamiliar code, often without understanding how it affects their take-home pay.

The 0T W1 tax code is one of several used by HMRC to calculate how much tax you should pay, particularly when your personal details are incomplete or there’s a temporary change in your employment situation.

In this guide, you’ll learn exactly what the 0T W1 tax code means, why you may have been placed on it, and how it impacts your income.

You’ll also discover what actions you can take to fix it and potentially claim back overpaid tax. Whether you’re starting a new job, switching roles, or unsure about your P45 status, this article breaks it down clearly so you can regain control over your pay and avoid further surprises.

What Is the 0T W1 Tax Code?

The 0T W1 tax code is often referred to as an emergency tax code, used when HMRC or your employer doesn’t have enough information about your income or previous tax status.

It tells the employer to deduct income tax from all of your earnings without applying any personal allowance. This means you don’t benefit from the usual tax-free threshold, which in 2025/26 is £12,570 under the standard 1257L code.

The “0T” part of the code signifies that no tax-free allowance is considered. Meanwhile, “W1” stands for Week 1, which means your tax is calculated on a non-cumulative basis, each pay period is treated independently, ignoring any prior income or tax already paid.

You might find yourself on this tax code if:

• You’ve started a new job without a recent P45
• You’ve moved between multiple jobs in a short time
• You’ve returned to work after a long gap
• Your employer has incomplete tax details for you

This code is usually temporary and will be updated once HMRC receives the correct information.

When and Why Might You Be Put on the 0T W1 Tax Code?

HMRC assigns the 0T W1 tax code when your employer lacks the necessary information to allocate a standard tax code. It’s a precautionary approach to ensure tax is still collected, even when your status is unclear. Several common scenarios can lead to being placed on this code.

Could a New Job or a Missing P45 Trigger This Tax Code?

Yes, starting a new job without providing a P45 is one of the most common reasons you might be assigned the 0T W1 code. The P45 gives your new employer your previous tax information, allowing them to apply the correct code.

Without it, your employer has no idea how much personal allowance you’ve already used in the tax year, so HMRC instructs them to tax all your income at standard rates without any allowance.

Employers must act quickly and usually default to this emergency code to ensure compliance. It remains active until HMRC or you provide the missing data.

What If You’re Retired or Have a Second Income?

Retirees returning to part-time work or people with more than one job may also be assigned the 0T W1 code.

Here’s why:

• Second Job: If your primary employment already uses your full personal allowance, your secondary employer might be instructed to use 0T W1, especially if tax records are incomplete.
• Retirement Income: When your pension provider and employer both try to use your tax-free allowance, one might default to 0T W1 while HMRC decides how to split your allowance correctly.

Additional reasons for being placed on 0T W1 include:

• Changing jobs mid-tax year
• Delays in updating records in HMRC systems
• Payroll system errors

It’s important to check your payslip regularly and report any discrepancies quickly.

How Does the 0T W1 Tax Code Affect Your Pay and Taxes?

The most significant impact of the 0T W1 tax code is that you receive no tax-free personal allowance. Your entire income is taxed from the very first pound earned. This can lead to noticeable reductions in your take-home pay. Under 0T W1, the tax is calculated using the current pay period only, ignoring any cumulative data.

Here’s how it breaks down:

This method often leads to over-taxation, especially for those on lower or average incomes, because the system cannot adjust for previous underpaid or overpaid tax periods. However, you may be eligible for a refund later once your tax code is corrected.

How Can You Tell If You’re on the Wrong Tax Code?

Recognising an incorrect tax code early can save you money. It’s always good practice to check your payslip each month for any unexpected changes.

Common signs you might be on the wrong tax code:

• Your payslip shows 0T W1, M1, or BR
• You earn less than the personal allowance but still pay income tax
• Your take-home pay is significantly lower than expected
• You’ve recently changed jobs or started multiple jobs

You can also use the HMRC online tax checker tool or your Personal Tax Account to verify your current tax code and ensure it matches your employment status.

How Do You Correct the 0T W1 Tax Code with HMRC?

Fixing the 0T W1 tax code is generally straightforward. The key is to provide accurate and complete information to either your employer or HMRC.

To correct the code:

• Submit a P45 to your new employer if you haven’t already
• Fill out a new starter checklist (formerly P46) if your P45 isn’t available
• Log in to your Personal Tax Account and update your employment details
• Call HMRC directly on 0300 200 3300 with your National Insurance number

Once the correct information is received, HMRC will issue a tax code notice (P6) to your employer, who should then adjust your code in the next payroll cycle. Corrections are typically reflected within 1–2 pay periods.

Can You Claim a Refund If You’ve Overpaid Tax on 0T W1?

Yes, if you’ve been on the 0T W1 tax code and overpaid tax, you’re likely eligible for a refund. HMRC reviews most cases automatically at the end of the tax year. However, if you’ve left your job or switched employers mid-year, you may need to claim it manually.

You can request a refund:

• Through your Personal Tax Account
• By completing a P50 form if you’re not working
• By calling HMRC directly

Refunds are usually issued via bank transfer or cheque within 8–12 weeks of the request or correction.

What Are the Differences Between 0T W1 and Other Tax Codes?

Understanding how 0T W1 differs from other tax codes helps clarify its impact.

Here’s a comparison:

The key difference with 0T W1 is the lack of tax-free allowance and the non-cumulative calculation, which often leads to overpayment.

What Can You Do to Avoid Being Put on a 0T W1 Code Again?

Being proactive with your tax information is the best way to avoid the 0T W1 tax code in the future.

Here’s how:

• Always provide your P45 when starting a new job
• Ensure your employer receives your correct National Insurance number
• Keep your HMRC Personal Tax Account updated
• Inform HMRC of multiple jobs or pensions
• If unsure, request a tax code review

Taking these simple steps ensures that your tax code is allocated correctly from the start of your employment, saving you from future corrections and overpayments.

Conclusion

The 0T W1 tax code can feel confusing and costly, especially if it appears unexpectedly on your payslip. While it’s generally a temporary measure, it can significantly impact your take-home pay by excluding your tax-free personal allowance and applying non-cumulative calculations.

Understanding why you’re on this code, how it works, and what actions you can take to fix it empowers you to stay in control of your finances.

Whether it’s submitting a missing P45, updating HMRC, or checking your Personal Tax Account, timely action can prevent overpayment and even unlock a tax refund. Stay informed, stay proactive, and you’ll navigate the 0T W1 code with confidence.

FAQs

What does W1 mean in a tax code?

W1 means Week 1. It refers to a non-cumulative tax calculation where each week’s income is taxed in isolation, ignoring what’s been paid or earned previously.

Is the 0T W1 code always a temporary tax code?

Yes, it’s designed to be temporary. It’s used when HMRC or your employer lacks full tax details and will usually be replaced once the correct data is submitted.

Can I end up overpaying tax with a 0T W1 code?

Yes, many people overpay tax when placed on 0T W1. However, HMRC allows for refunds once your records are corrected.

How do I know if I’ve been overtaxed?

Check your payslip for unexpected deductions, and compare it with the standard 1257L allowance. You can also verify your tax records via your HMRC Personal Tax Account.

What should I do if I see 0T W1 on my payslip?

Contact your employer to check if your P45 or new starter information was submitted. You may also contact HMRC directly for clarification and correction.

Do I need to claim a refund or will HMRC do it automatically?

Often, HMRC processes refunds automatically at year-end. But if you’ve changed jobs or left employment, it’s advisable to claim directly to avoid delays.

Can my employer correct my tax code?

Employers can only apply the code provided by HMRC. If your tax code is wrong, you’ll need to update your details with HMRC so they can issue a corrected code.