What Does “Week 1/Month 1” Mean on My Payslip

Introduction

Every UK payslip includes a tax code, which tells your employer how much Income Tax to deduct under PAYE (Pay As You Earn). Occasionally, you might see the phrase “Week 1” or “Month 1” after your tax code, such as “1257L W1” or “1257L M1.”

This notation indicates that you are on a non-cumulative tax basis, sometimes called an emergency tax code. It means HMRC is instructing your employer to calculate your tax as if each payday is the first one of the tax year, without taking into account what you have already earned or paid in previous months.

What “Week 1” and “Month 1” mean

The PAYE system usually works on a cumulative basis, meaning your tax is calculated based on your total earnings and tax paid since the start of the tax year (6 April). This ensures you get the right personal allowance spread evenly across the year.

However, if you are on a “Week 1” or “Month 1” tax code:

Your employer calculates tax only on that week’s or month’s pay.

Previous earnings and deductions are ignored.

You get one week’s or one month’s worth of personal allowance each time you are paid.

This approach prevents HMRC from accidentally over-refunding or under-collecting tax when your income details are unclear.

When you might see “Week 1/Month 1” on your payslip

You might be placed on a Week 1 or Month 1 code in several situations, such as:

Starting a new job: If your new employer does not have your P45 from your previous employer, HMRC cannot yet confirm your tax history, so a temporary code is applied.

Changing from self-employment to employment: HMRC may use a Week 1 or Month 1 code until your new employment details are established.

Multiple jobs or pensions: If you have more than one source of income, HMRC may use a non-cumulative code to prevent overlapping tax allowances.

Tax code change mid-year: If HMRC issues a new code due to a change in circumstances, the first few months may be on a Week 1/Month 1 basis.

It is not usually permanent and should be updated once HMRC has the correct information.

How Week 1/Month 1 affects your pay

Being on a Week 1 or Month 1 tax code can cause temporary overpayments of tax. Because the code resets your personal allowance each pay period, it ignores previous pay and tax, which can lead to slightly higher deductions.

For example, if you have earned less than your full annual tax-free allowance so far, a cumulative code would reduce your tax bill accordingly. Under a Week 1 or Month 1 code, that adjustment does not happen until your code is corrected.

The difference can vary depending on your pay and when in the tax year the code is applied.

Is it the same as emergency tax

Yes, “Week 1” or “Month 1” is sometimes referred to as an emergency tax code. This does not mean you are doing anything wrong; it simply means HMRC is using a temporary method to collect tax until your details are updated.

Common emergency tax codes include 1257L W1/M1 or 0T W1/M1. These codes allow you to keep earning while HMRC sorts out your full records.

How to fix a Week 1 or Month 1 tax code

You do not need to do anything immediately if you see “W1” or “M1” on your payslip, but you should make sure HMRC has your correct employment details.

To help speed things up:

Check your P45: If you have one from your previous job, give it to your new employer as soon as possible.

Contact HMRC: If you do not have a P45, or if you think your code is wrong, call HMRC on 0300 200 3300 or update your details in your Personal Tax Account online.

Wait for your new code: Once HMRC has confirmed your income history, they will issue an updated, cumulative tax code to your employer automatically.

When your code changes, your employer will adjust your pay to reflect any overpaid or underpaid tax from earlier in the year.

How long it lasts

A Week 1 or Month 1 code is temporary. Once HMRC receives all your pay and tax information, it will issue a normal cumulative code that ensures you receive the correct annual tax allowance.

This usually happens within a few weeks, although it can take longer if HMRC needs to gather data from previous employers or pension providers.

Will I get a refund

If you have overpaid tax because of a Week 1 or Month 1 code, you will get a refund automatically once your code is corrected. This can happen either:

In your next payslip, if your employer adjusts your tax through payroll.

Directly from HMRC, if the correction happens after you leave your job.

You do not need to submit a tax return unless you are self-employed or have complex income sources.

How to check your tax code

You can check your current tax code by:

Looking at your latest payslip (it appears next to your tax deductions).

Reviewing your P45 or P60.

Logging into your Personal Tax Account on GOV.UK.

If your payslip shows a code ending with “W1” or “M1,” it means your tax is being calculated on a non-cumulative basis.

Common mistakes to avoid

Ignoring your payslip and not checking your tax code.

Assuming a Week 1/Month 1 code is permanent.

Failing to provide a P45 to your new employer.

Waiting too long to contact HMRC if your tax seems too high.

Checking your code early can prevent overpayment and ensure you receive any refunds quickly.

Conclusion

Seeing “Week 1” or “Month 1” on your payslip simply means you are on a temporary, non-cumulative tax code. It is a common situation when starting a new job or changing employers.

While you might pay a little more tax initially, HMRC will correct your tax code once your full employment record is confirmed. Any overpaid tax will be refunded automatically, ensuring you pay the right amount by the end of the tax year.

Always check your payslips regularly and keep HMRC updated with accurate information to avoid tax code errors in the future.