What is the M1 Tax Code? Emergency Tax Explained

The M1 tax code on your payslip can be concerning, especially if your take-home pay suddenly decreases. In most cases, the M1 tax code is linked to emergency tax, meaning your employer temporarily taxes your income on a month-by-month basis rather than cumulatively across the tax year.

This typically occurs when HM Revenue and Customs (HMRC) or your employer does not have your complete payroll information. Moreover, it often happens after you change jobs, start a new role, or begin receiving additional income.

What is the M1 Tax Code in the UK?

In the United Kingdom, the M1 tax code is often referred to as an “emergency tax code”. It is used temporarily until HMRC has the necessary information to issue the appropriate tax code. This usually happens when an individual begins a new job without a P45.

The key characteristic of the M1 tax code is that it is “non-cumulative.” This means it does not take previous pay or tax deductions from the current tax year into account. Rather than calculating your tax based on your total earnings and tax-free allowance, it resets the calculation each month.

What is the Meaning of 1257l M1?

One of the most commonly seen versions of the M1 code is 1257L M1. The significance of each component is as follows:

• 1257: This represents the standard Personal Allowance of £12,570 for the 2026/27 tax year. HMRC removes the final digit when creating tax codes, which is why £12,570 becomes 1257.
• L: This indicates that you are entitled to the standard Personal Allowance, which is tax-free.
• M1: This confirms that the code is non-cumulative and is calculated on a month-by-month basis.

Is 1257l/M1 an Emergency Tax Code?

Yes, in the UK, the standard tax code for the personal allowance is 1257L, which applies to most employees. However, “M1” indicates that your tax is calculated on a Month 1 basis. This means each month is treated separately instead of using cumulative earnings across the tax year. It typically occurs when your employer or HMRC lacks complete payroll information.

The most common reasons are the following:

• Starting a new job without a P45,
• Transitioning from self-employment to employment,
• Receiving taxable benefits or pension income, or
• Waiting for updated HMRC records.

Why Has My Tax Code Suddenly Changed To M1?

HMRC does not randomly assign the M1 tax code. You may receive it for a variety of reasons.

Starting a New Job

One of the most common reasons for M1 is starting a new job. If your new employer fails to receive a P45 from your previous employer on time, they are unable to determine the amount of tax you have already paid.

To prevent payroll errors, HMRC or your employer may temporarily apply the M1 tax code. HMRC or your employer may implement M1 as a holding code until the right information is received.

Self-Employed Or Multiple Sources Of Income

HMRC may apply M1 to one of your employments while they determine how to correctly split your Personal Allowance. This is often done to prevent underpayment, particularly if you are self-employed or have multiple PAYE income sources. Typically, HMRC applies the entire Personal Allowance to your employment income through PAYE, while taxing your self-employment profits separately through Self Assessment.

HMRC Updated Your Payroll Information

Occasionally, HMRC modifies your tax code during the tax year. This may occur if you begin receiving company benefits, change jobs, or experience fluctuations in income. HMRC may use M1 to prevent your employer from recalculating all the tax when a code changes mid-year. It could result in a sudden underpayment or overpayment.

Returning to Work After a Career Break

HMRC may not have the most recent earnings information on file if you have been unemployed for an extended period and are now returning to work. The M1 tax code is used to ensure that you are taxed safely until HMRC can verify your circumstances.

How Long Do You Stay On The M1 Tax Code?

The M1 tax code is usually corrected after your employer submits the correct PAYE information or processes your P45. In many cases, the M1 tax code is corrected within a few weeks or after one or two payroll cycles. However, more complex situations may take longer to resolve. A new cumulative tax code is typically issued automatically after HMRC updates your records. If you paid an excessive amount of tax while under the M1 tax code, the overpayment is frequently refunded directly through your salary.

How Much is The Emergency Tax M1 HMRC?

Tax code 1257L M1 implies that you receive only 1/12 of the annual Personal Allowance of £12,570 per year, which is £1,048 tax-free per month. Income earned above the monthly allowance is subject to tax at the relevant income tax rates of 20%, 40%, or 45%. Sometimes, temporary overpayments may result from the M1 tax code, as it does not account for previous pay or tax deductions already taken during the year.

PAYE Tax Rate	Rate of Tax	Taxable Income Band (England & Northern Ireland)
Basic tax rate	20%	Up to £37,700
Higher tax rate	40%	From £37,701 to £125,140
Additional tax rate	45%	Above £125,140

Let’s understand this with an example:

If you earn £4,000 in a month, your employer uses your tax code (typically 1257L) to compute your income tax, as per the 2026/27 UK tax rules. After applying the Personal Allowance, the remaining income is then taxed at 20%.

How To Check If Your M1 Tax Code is Correct?

To verify your M1 tax code, review your payslip and compare it to previous payslips to identify any recent changes. It is also helpful to check your HMRC Personal Tax Account, which provides access to your current employment and tax information.

In some cases, your payroll department may be able to confirm why the M1 tax code has been applied and whether any updates are still pending. You should contact HMRC directly if the tax code appears to be incorrect or if you believe you are paying an excessive amount of tax. HMRC can update your employment information and review your tax records to ensure the correct tax code is applied.

How Do You Fix the M1 Tax Code?

There are several steps you can take if you have been assigned the M1 tax code. The issue is typically temporary and can be corrected once HMRC receives the correct payroll and employment information.

• The quickest way to update your tax code is to provide your P45 to your new employer, as it contains your previous pay and tax details.
• If you do not have a P45, you can update your employment details online using HMRC’s “Check your Income Tax” service or the HMRC app.
• Ensure you complete your starter checklist or new starter form accurately, as inaccurate information can trigger an emergency tax code.
• If your tax code remains unchanged after one or two payroll cycles, you may need to contact HMRC directly. To speed up the process, ensure that you have your employer details, PAYE reference, and National Insurance number readily available.

Does M1 Always Mean You Are Overpaying Tax?

No, an M1 tax code does not necessarily indicate that you are permanently overpaying tax. However, it can temporarily result in overpaying taxes for a particular pay period.

The positive aspect is that any overpaid taxes are typically corrected automatically as your tax situation updates, with refunds frequently being processed through your payroll. In certain instances, you may also be able to claim back any excess tax directly from HMRC.

Got M1 Tax Code Issues? Let Professionals Handle Your Payroll

Managing payroll, tax codes, dividends, and compliance with HMRC can quickly become complex, particularly if you operate through a limited company or work as a contractor. At LimitedCompanyAccountants, we help ensure you remain fully compliant while correctly managing payroll and PAYE, helping to prevent payroll issues such as incorrect emergency tax codes. We also help you manage corporation tax efficiently and maximise allowable expenses.

Get professional accounting support for just £399.00 + VAT with our One-Off Package and take control of your limited company finances today.

The Bottom Line

The M1 tax code is not necessarily an error; however, it frequently suggests that HMRC or your employer is working with incomplete payroll information. Although it is commonly referred to as an emergency tax code, it is typically temporary, and HMRC can resolve it promptly once the records are updated.

It is advisable to verify your tax code, particularly if you have recently changed jobs, started receiving new income, or observed unusual deductions from your payslip. This can help ensure that you are not paying excessive taxes.