UK Tax Codes Explained: What 1257L, BR, K, and NT Mean

Your HMRC tax code is the single most crucial string of letters and numbers on your payslip. Issued by HM Revenue and Customs (HMRC) to your employer or pension provider, your tax code dictates exactly how much income you can earn completely tax-free each pay period. If your tax code is incorrect, you could be silently losing hundreds of pounds in overpaid tax every month or building an unexpected tax debt.

1. How to Read and Decode Your UK Tax Code

A standard UK tax code consists of numbers followed by a letter (or in special cases, a letter prefix). For the 2026/27 tax year, the standard tax code for an employee with one job is 1257L:

• The Numbers (1257): Multiply the numbers by 10 to determine your tax-free Personal Allowance for the year. 1257 × 10 = £12,570 tax-free.
• The Letter (L): Indicates that you are entitled to the standard Personal Allowance for someone born after 5 April 1948.

2. Complete HMRC Tax Code Letter Reference Table

To verify what your current tax code means for your net pay, use our free Tax Code Calculator.

3. How to Fix an Incorrect Tax Code Online

If your payslip displays an incorrect code (such as BR, 0T, or an unexplained K code), do not rely on your employer’s payroll department to fix it. Employers are legally prohibited from altering tax codes without an official P6 coding notice from HMRC.

Follow these steps to correct your tax code immediately:

1. Log into your HMRC Personal Tax Account via the Gov.uk portal or the official HMRC App.
2. Navigate to the ‘Pay As You Earn (PAYE)’ section and click ‘Check your current tax code’.
3. Click ‘Update estimated taxable income’ or remove taxable benefits that you no longer receive.
4. HMRC will automatically issue an electronic P6 coding notice to your employer, and any overpaid tax will be refunded in your subsequent paycheck!

5. Detailed Breakdown of Complex Tax Code Scenarios

Certain employment situations generate specialized tax codes that require careful monitoring:

• Tax Code K450: A K prefix code means untaxed income or taxable perks exceed your personal allowance by £4,500. Payroll adds £4,500 of notional income across the tax year to calculate higher PAYE deductions. HMRC caps K-code deductions so that tax cannot exceed 50% of your gross pay in any pay period.
• Tax Code 0T: Implemented when starting a job without a P45 or when income exceeds £125,140. It offers zero tax-free allowance while applying 20%, 40%, and 45% tax bands progressively.
• Tax Code NT: No Tax code issued for non-resident mariners, foreign diplomats, or specific statutory compensation payouts.

6. How to Reconcile Tax Codes Across Job Changes

When switching employers, ensure your previous employer issues your official Form P45 promptly. Part 1 is submitted electronically to HMRC, while you hand Parts 2 and 3 to your new employer. If your new job begins before receiving your P45, complete an official HMRC Starter Checklist immediately to avoid being placed on emergency code 0T.

4. Frequently Asked Questions (FAQ)

Q: What should I do if my tax code is 1257L W1?
A: The W1 suffix means you are on an emergency week 1 (non-cumulative) tax code. Provide your P45 to payroll or update your income in the HMRC app to switch to the standard cumulative 1257L code.

Q: Why does my tax code have a K prefix?
A: A K prefix means your total untaxed income or company benefits (such as a company car or fuel allowance) exceed your £12,570 Personal Allowance. The number after the K represents the extra taxable income added to your pay.

Q: Can payroll change my tax code if I ask them?
A: No. By law, UK employers can only change an employee’s tax code upon receiving an official electronic P6 or P9 coding notice directly from HMRC.

Q: Why did my tax code change without warning?
A: HMRC regularly reviews employer Real Time Information (RTI) data. If you received a pay rise, started a company benefit, or owed underpaid tax from a prior year, HMRC updates your code automatically.

Q: What is the difference between tax code BR and 0T?
A: Code BR taxes 100% of income at a flat 20% Basic Rate. Code 0T provides £0 allowance but applies all marginal tax brackets (20%, 40%, and 45%) as your pay increases.

Q: What does tax code 1257L M mean?
A: It means you receive the Marriage Allowance: your spouse transferred £1,260 of their unused allowance to you, giving you an increased tax-free allowance of £13,830 (code 1383M).

Q: How do Scottish tax codes work?
A: Scottish tax codes begin with an ‘S’ prefix (e.g. S1257L) and calculate tax according to the Scottish Parliament’s 6-band income tax structure.

Q: How long does it take for HMRC to refund tax after correcting my code?
A: Once HMRC issues the new coding notice, your employer’s payroll software will automatically calculate the cumulative refund and include it in your next normal paycheck (usually within 30 days).

Q: What does tax code 1257L C mean on a payslip?
A: The ‘C’ prefix indicates that you are a Welsh taxpayer (Code C1257L). While the Welsh Government holds devolved powers to vary income tax rates, they have historically aligned Welsh rates identically with England.

Q: Why has HMRC placed me on a K tax code?
A: A K prefix code occurs when your taxable company benefits (such as private healthcare or a high-emission company car) exceed your statutory £12,570 Personal Allowance, creating negative allowances where extra tax is deducted from your wages.