What a tax code does
Who this guide is for: Helpful when checking a payslip code, starting a second job, or using the Income Tax Calculator's tax-code interpretation.
Your tax code tells payroll how much Income Tax to deduct under PAYE. It reflects your Personal Allowance and adjustments such as benefits in kind or unpaid tax collected via your wages.
For 2026/27, the standard code in Northline's tax-year config is 1257L. Interpretations below use the same shared tax-code parser as the Income Tax Calculator.
Common codes explained
| Code | What it usually means | When it may appear | What to check |
|---|---|---|---|
| 1257L | Standard cumulative tax code | Common for a single employment with the standard Personal Allowance. | Matches your Personal Tax Account and expected allowance. |
| BR | All pay taxed at basic rate | Often a second job, or when allowance is used elsewhere. | Confirm which job holds your Personal Allowance. |
| D0 | All pay taxed at higher rate | Typically when allowance and basic-rate band are used on another income. | Expected if you already use basic-rate room elsewhere — not always an error. |
| D1 | All pay taxed at additional rate | Less common; used when lower bands are fully used elsewhere. | Compare with total income and other employments. |
| 0T | No Personal Allowance | Starter situations, emergency treatment, or allowance used elsewhere. | Whether a full cumulative code should replace it. |
| K500 | Negative allowance tax code | Benefits, underpaid tax collected via payroll, or similar adjustments. | Whether the K adjustment matches known benefits or underpayments. |
| NT | No Income Tax deducted | Specific situations where payroll should not deduct Income Tax. | Confirm with HMRC if unexpected — uncommon for most employees. |
| 1257L M1 / W1 | Same base code operated on a non-cumulative (month-1 / week-1) basis. | Often temporary after starting a job or until records catch up. | See Emergency Tax Codes Explained if it persists. |
| X suffix | Non-cumulative marker used in some payroll presentations. | Alongside emergency or week-1 / month-1 treatment. | Whether HMRC has issued a cumulative code yet. |
| S1257L | Scottish prefix — Scottish Income Tax bands apply to non-savings income. | HMRC treats you as a Scottish taxpayer. | Residence status, not where your employer's office is. |
| C1257L | Welsh (C) prefix — Welsh taxpayer coding. | HMRC treats you as a Welsh taxpayer. | Personal Tax Account shows the expected nation. |
Check it against your situation
A wrong code can under- or over-deduct tax all year. Compare the code with your Personal Tax Account and update HMRC if benefits or jobs have changed. For how bands interact with allowance, see Income Tax Bands Explained.
Interpret your tax code and estimate take-home pay Use the Income Tax Calculator