Your salary has stayed the same, but your take-home pay has dropped. Before assuming payroll has made a mistake, check the tax code on your payslip.
A tax code tells your employer or pension provider how to calculate Income Tax. It reflects the information HMRC holds about your income and allowances. If that information is incomplete or out of date, the deductions from your pay could be wrong.
Understanding UK tax codes helps you spot problems and know who to contact. This guide covers common codes, emergency tax and the steps to take when something does not look right.
The figures below relate to the 2026/27 tax year, which runs from 6 April 2026 to 5 April 2027.
What Does the 1257L Tax Code Mean?
1257L is the code used for most people with one job or pension. It normally gives that income source the standard £12,570 tax-free allowance.
The number represents the allowance used in the payroll calculation. The letter identifies the type of allowance or tax treatment.
However, 1257L is not the correct code for everyone. Your code can reflect adjustments for benefits, other income or tax owed.
You will also see regional prefixes. S indicates Scottish Income Tax treatment, while C indicates Welsh treatment.
The standard Personal Allowance reduces by £1 for every £2 of adjusted net income above £100,000. It reaches zero at £125,140. This is one reason a higher earner should not assume they are entitled to the full allowance.
Common UK Tax Codes Explained
These are some of the codes and letters you are likely to encounter.
| Code or letter | What it means |
| BR | All income from this job or pension is taxed at the basic rate |
| D0 | All income from this source is taxed at the higher rate |
| D1 | All income from this source is taxed at the additional rate |
| 0T | No Personal Allowance is applied |
| M | You receive a Marriage Allowance transfer |
| N | You transfer part of your allowance to your spouse or civil partner |
| NT | No Income Tax is deducted from this income |
BR, D0 and D1 have regional variations. Scottish codes use different bands, so check the complete code rather than reading only the final characters.
What Is Emergency Tax?
Emergency tax uses your income for the current pay period without reconciling earlier pay and tax in the same year.
Look for these markers:
- W1 for a weekly calculation.
- M1 for a monthly calculation.
- X for varying pay dates.
- NONCUM, which some payroll systems display.
For example, 1257L M1 uses a monthly emergency basis. 1257L on its own is not an emergency tax code.
This often happens when a new employer does not yet have your previous income details. HMRC also uses emergency codes in some other circumstances, including changes involving company benefits or the State Pension.
Emergency tax is not a separate tax rate. Its effect depends on the code, your earnings and what happened earlier in the year.
How Emergency Tax Affects a Payslip
Consider an employee in England who starts work in October 2026. They have had no taxable income since 6 April and receive £2,000 a month.
Assume they qualify for the full Personal Allowance and have no other adjustments.
Under a simplified 1257L M1 calculation:
| Monthly calculation | Amount |
| Gross pay | £2,000 |
| Approximate monthly allowance | £1,047.50 |
| Pay above that allowance | £952.50 |
| Approximate Income Tax at 20% | £190.50 |
With a correct cumulative code and the earlier income position confirmed, unused allowance from previous months would be considered. In this example, it would cover the October salary, leaving no Income Tax due on that payment.
The illustration uses the current allowance and basic rate. Payroll rounding can produce small differences. National Insurance, pension contributions and other deductions are excluded.
Why Your Tax Code Changes
A new code does not automatically indicate an error.
HMRC updates codes when circumstances change. Common reasons include another job, a new pension, a company benefit or a change to Marriage Allowance. A code can also collect tax owed from an earlier period.
Check the explanation behind the change.
For example, if you stopped receiving private medical insurance, check whether HMRC still includes it. If an old job remains active in your tax records, check that the leaving details have been reported.
Comparing your code with a colleague’s is less useful. Two people earning the same salary can have different allowances and adjustments.
What a K Tax Code Means
A K code applies when the deductions included in your code exceed your tax-free allowance.
This can arise from company benefits, untaxed income or tax being collected through your wages or pension.
Instead of providing a tax-free amount, the code adds an amount to the income used for the tax calculation. It does not mean your employer has paid you that extra money.
When using a K code, the employer or pension provider cannot deduct more than half of your pre-tax pay or pension as Income Tax.
If the code is unfamiliar, review HMRC’s breakdown. The underlying figures matter more than the letter alone.
How to Check and Correct Your Tax Code
Start with your latest payslip and HMRC’s Check your Income Tax online service.
Review your employment and pension records, estimated taxable income, company benefits and expenses. Correct anything missing or inaccurate.
If HMRC decides the code needs changing, it says it will notify you and your employer within 15 working days. Monthly-paid employees should normally see the new code on their next or following payslip. For weekly pay, it should appear on the third payslip.
Keep a short record of the issue:
- The code shown on the payslip.
- The code shown by HMRC.
- The pay period affected.
- Any change in employment or benefits.
- When you updated your details.
If HMRC shows a new code but payroll still uses the old one, ask your employer whether they received the notice. If both show the same code but its calculation is wrong, review the information held by HMRC.
What to Do When Starting a New Job
Give your new employer your P45. If you do not have one, complete the starter checklist accurately.
The checklist asks about your employment and benefits position. Choose the statement that reflects your circumstances. Guessing an answer because it appears to produce less tax can create a problem later.
Employers use the P45 or starter information to establish the initial payroll treatment.
For a new job, HMRC says updating the code can take up to 35 days while it receives the necessary details. If the code still looks wrong after that period, check your records and follow the correction process.
How an Emergency Tax Refund Works
A refund depends on whether you have actually overpaid.
Once HMRC has the necessary income information, it checks the tax deducted against the amount due. Where a correction produces an overpayment, the employer or pension provider normally refunds it through pay when applying the updated code.
If the tax year has ended, HMRC reviews the annual position and explains how to obtain any repayment due. Missing income details can delay the calculation.
The result can also be an underpayment. In that case, HMRC explains how the outstanding tax will be collected.
Check the tax deduction and year-to-date totals on the payslip showing the correction. Do not rely only on the amount paid into your bank account.
Common Questions About Tax Codes
Is BR always the wrong code?
No. It is often appropriate for a second job or pension where the Personal Allowance is used elsewhere. It needs checking if your overall circumstances do not support that treatment.
Why has my pay fallen when the code has not changed?
Compare the whole payslip. Look at gross pay, overtime, pension deductions, student loan deductions and any unpaid leave.
A tax code is only one part of the calculation. Mark the figures that changed before contacting payroll.
Should I wait until the end of the year?
You can check and update incorrect information during the tax year. For a recent job change, allow for HMRC’s new-starter processing period. You do not need to leave a known error unreported until April.
Get Help Understanding Your Tax Code
If you cannot explain a change in your tax deductions, speak to RMA Accountants.
Bring your latest payslips, any P45 or P60, and the tax-code notice from HMRC. Details of other jobs, pensions and company benefits will also help establish whether the code matches your circumstances.
