UK tax codes, explained

Your tax code tells your employer’s payroll software how much tax-free pay you should receive over the tax year, and which Income Tax rules apply. Most UK employees on a single job with standard allowance see 1257L in 2025/26. Many do not — second jobs, benefits-in-kind, underpaid tax from previous years, Scottish residency, and emergency defaults all change the code. A wrong code does not change your final annual tax bill forever — PAYE is reconciled — but it can make individual months painful.

This guide decodes common UK tax codes for 2025/26: 1257L, BR, D0, D1, K codes, the Scottish S prefix, cumulative vs W1/M1 bases, and when to open your Personal Tax Account. For payslip line labels see reading a payslip; for new-job BR shock see emergency tax.

How tax codes are built

HMRC issues codes to employers. The number usually equals tax-free allowance ÷ 10. Letter suffixes modify behaviour:

• 1257 → £12,570 personal allowance (2025/26 standard)
• L → standard cumulative allowance
• M / N → Marriage Allowance received (M) or transferred (N)
• T — other calculations needed (HMRC review)
• 0T — no allowance; normal band rates on all taxable pay

Official reference: gov.uk/tax-codes and tax code letters.

1257L — the default most people expect

1257L means:

• £12,570 tax-free income spread across the year
• Cumulative PAYE — under- or over-tax earlier months adjust in later months
• England/Wales/NI Income Tax bands (20%, 40%, 45%)

On £50,000 gross with 1257L, annual Income Tax ≈ £7,486, employee NI ≈ £2,994, take-home ≈ £39,520 (~£3,293/month). TaxBite default scenario.

S1257L — Scottish Income Tax

The S prefix tells payroll to apply Scottish Income Tax bands and rates — not England/Wales/NI. Allowance is still £12,570; NI unchanged. At £50,000 gross, Scottish tax is higher — take-home ≈ £37,990/year vs ~£39,520 in England (~£127/month gap). See Scotland vs England.

If you moved to Scotland mid-year, HMRC should update to S codes. Still seeing plain 1257L in Edinburgh? Check Personal Tax Account — wrong region costs real money.

BR — Basic Rate, no allowance on this job

BR taxes all pay from this employment at 20% with no personal allowance allocated to it. Common when:

• Second job (allowance on main job)
• Emergency tax on new starter without P45
• HMRC has not processed starter information

At £50,000 on BR all year: Income Tax = 20% × £50,000 = £10,000 vs £7,486 on 1257L — over-tax ≈ £2,514/year (~£209/month). NI identical. BR is often temporary on first jobs; on second jobs it may be correct annually.

Model: TaxBite BR · Guide: emergency tax

D0 and D1 — emergency higher/additional rate

D0 — all pay taxed at 40% (higher rate flat). No allowance. Devastating on a £50k salary if left uncorrected: tax ≈ £20,000/year vs ~£7,486 normal — net pay can fall toward £2,250/month in simplified models.

D1 — all pay at 45% (additional rate flat). Rare on moderate salaries; indicates HMRC treating employment as fully additional-rate until corrected.

Both are emergency-style flat codes. If your payslip shows D0 on £50k, contact payroll immediately with Personal Tax Account screenshot.

0T — zero allowance, normal bands

0T gives no personal allowance but taxes through progressive bands (20%, then 40%, then 45%) rather than flat BR. On low/medium salaries 0T can be harsher than 1257L; on very high salaries it may be closer to correct than BR. Often appears when allowance is exhausted elsewhere or HMRC lacks information.

K codes — when you owe tax on extra income

A K prefix means negative allowance — taxable benefits or underpaid tax from prior years exceed free pay. Payroll adds the K number × 10 to taxable pay before calculating tax.

Example: code K500 → add £5,000 to taxable pay. On £50,000 salary, tax computed as if you earned £55,000 for PAYE purposes (simplified). Common triggers:

• Company car benefit-in-kind
• Private medical insurance
• Underpaid tax from previous year
• Multiple untaxed income sources

K codes are not punishments — they collect tax that would otherwise be due via Self Assessment. Ignoring them builds debt.

W1 and M1 — week 1 / month 1 non-cumulative

Suffixes W1 (week 1) or M1 (month 1) mean payroll ignores year-to-date — each period taxed in isolation. Example: 1257L M1 applies one month’s allowance to that month only, not cumulatively. Can over-tax early in the year or under-tax bonuses unpredictably. Often paired with emergency situations.

Cumulative 1257L vs 1257L M1 on a £5,000 bonus month: cumulative may spread shock; M1 may tax bonus aggressively without YTD smoothing. See bonus tax guide.

Other codes you might see

• NT — no tax (specific circumstances; not “free money forever”)
• C prefix — Welsh rates (mirrored England for 2025/26 bands in practice)
• SD0, SD1, SD2, SD3 — Scottish emergency/devolved flat codes in some payroll systems
• 1257L with reduced number — e.g. 1000L if allowance partially used elsewhere

Worked comparison: £50,000 salary, month 1

Gross £4,167 — Income Tax only (NI ~£250 both cases):

Scotland higher tax shows even on “normal” S1257L — not an error. BR/D0 on month one is often fixable; S prefix is structural if you live in Scotland.

Multiple jobs — splitting allowance

You have one personal allowance per tax year — usually applied to your main job. Second job often gets BR or a reduced number code. Total annual tax can still be correct if combined income is taxed properly across employments. Problems arise when:

• Both jobs use full 1257L — under-tax until HMRC catches up
• BR on second job but first job under £12,570 — over-tax until adjusted

Personal Tax Account shows how HMRC allocated allowance across employments.

Benefits-in-kind and code changes

Company car, medical cover, living accommodation — HMRC adjusts code to collect tax on cash-equivalent benefits without you paying separately. You may never see a deduction line; tax simply rises via lower allowance or K code. TaxBite does not model BIK; if your code dropped from 1257L to 1000L mysteriously, check benefits on P11D.

When to check Personal Tax Account

Open Personal Tax Account (HMRC app or web) when:

1. Starting a new job — within 2 weeks of first payslip
2. Code is BR, D0, 0T, or K — and you do not know why
3. Net pay changed with no salary change
4. Moving to or from Scotland — S prefix should appear or disappear
5. Crossing £100,000 — allowance taper may shrink code mid-year
6. After bonus — if code still M1 months later
7. Annual review — each April after P60

You can sometimes update estimated income or report changes online; payroll cannot change codes HMRC has not issued.

How to fix a wrong code

1. Check Personal Tax Account for HMRC’s code and explanation
2. Give payroll your P45 or complete starter checklist accurately
3. Call HMRC if employer code disagrees with your understanding
4. Payroll applies updated code when HMRC transmits it — not before
5. Over-tax usually corrects via lower tax later or refund after year end

Keep payslips and P60. Under-payment may require payment plan — ignoring K codes makes it worse.

Tax codes vs actual annual liability

PAYE codes are a collection mechanism. Your true liability depends on total income, allowances, benefits, and region. Code fixes cash flow; Self Assessment reconciles complex cases. If you have rental income, significant dividends, or sole trade on the side, code alone may not capture everything — register for Self Assessment if required.

£100k taper and your code

Above £100,000, allowance tapers to zero at £125,140. HMRC may reduce code proactively (e.g. below 1257) or issue K-style adjustments. Effective marginal rates hit 60%+ on some slices — £100k guide. If bonus pushes you over £100k mid-year, code may lag until HMRC catches up.

Decoding the number — worked examples

If your code is 1000L, allowance ≈ £10,000 — HMRC has allocated £2,570 elsewhere (often a second job or benefit adjustment). If 1185L, allowance ≈ £11,850 — partial use. The maths: multiply code number by 10 for annual tax-free pay (before K adjustments).

Marriage Allowance codes: M suffix means you receive 10% of partner’s allowance; N means you transferred 10%. Eligibility rules on gov.uk — income limits apply.

Case study: new starter, code journey

Month 1: BR on £50k — net ~£3,084. Month 2: payroll receives 1257L from HMRC — cumulative PAYE catches up; month 2 tax may be lower than “normal” because YTD overpayment is absorbed. Month 6: steady ~£3,293 net. Without checking Personal Tax Account in month 1, you might assume salary was misquoted — when code was the issue.

Case study: company car and K code

Salary £45,000 plus company car BIK £5,000 → HMRC might issue K500. Tax calculated on effective £50,000 slice for PAYE even though cash salary is lower. Payslip gross still shows £45,000; tax line looks “high”. Fix is not salary negotiation — it is understanding BIK is taxed through code. TaxBite will not mirror this unless you model higher effective gross manually.

Scottish codes beyond S1257L

Scottish taxpayers may see SBR, SD0, SD1, SD2, SD3 in emergency or flat-rate situations — Scottish devolved equivalents of BR/D0-style treatment in some payroll systems. If you work in England for a Scottish employer or remotely cross-border, address on HMRC record drives S prefix — not office postcode alone.

Common myths

• “BR means I’m on basic rate tax forever” — BR is a collection shortcut, not your marginal rate destiny
• “Lower code = HMRC punishing me” — usually benefits or prior underpayment, not random
• “I can pick my own code” — payroll must use HMRC-issued code
• “Scottish codes only affect high earners” — S1257L changes tax from first pound above allowance

Model tax codes in TaxBite

Advanced Features accept overrides — compare normal vs emergency paths on your salary:

Emergency tax → · Reading a payslip → · How take-home works →

Estimates only — not tax advice. HMRC issues authoritative codes; payroll systems implement them with minor rounding differences. Benefits-in-kind and multi-job splits may require professional review.