The anatomy of a UK tax code
A UK tax code packs two pieces of information into a short string:
- A number — your tax-free Personal Allowance, divided by 10
- One or more letters — describing your circumstances
So 1257L = £12,570 personal allowance (1257 × 10) + L (standard circumstances).
The number portion tells your employer how much of your income to treat as tax-free each year. The letter tells them how the calculation should behave — whether to apply the allowance, ignore it, add extra income, tax everything at a flat rate, or run on emergency basis.
The numbers — what they mean
The number is your annual Personal Allowance divided by 10:
| Code number | Allowance | Notes |
|---|---|---|
| 1257 | £12,570 | Standard 2026/27 allowance |
| 1131 | £11,310 | Gave 10% Marriage Allowance to spouse (1131N) |
| 1383 | £13,830 | Received 10% Marriage Allowance from spouse (1383M) |
| 957 | £9,570 | Benefits in kind reducing allowance |
| 0 | £0 | No personal allowance applied (0T code) |
| K-prefix | Negative | Allowance is exhausted; additional income added |
The personal allowance is frozen at £12,570 through April 2031, so 1257 is the dominant numeric for most workers throughout the rest of the decade.
The standard letters (suffix)
L — Standard
The most common letter. Means: you get the standard personal allowance with no special adjustments. Most employees with one job and no taxable benefits see L. Full guide to 1257L →
M — Marriage Allowance received
You've received 10% of your spouse or civil partner's personal allowance via Marriage Allowance. Your tax-free allowance is £1,260 higher than standard. Code typically reads 1383M. Read about tax code M →
N — Marriage Allowance given
You've transferred 10% of your personal allowance to your spouse or civil partner. Your tax-free allowance is £1,260 lower than standard. Code typically reads 1131N. Read about tax code N →
T — Tailored / Top-rate review
A "T" suffix means HMRC has tailored your code with specific adjustments — often because your income exceeds £100,000 (where personal allowance tapers) or there are other items HMRC needs to monitor. The number reflects the adjusted allowance.
0T — No allowance
Used when HMRC believes you have no entitlement to a personal allowance. Common situations: a second job with no allowance to spare, an income exceeding £125,140 where the allowance is fully tapered, or insufficient information from a previous employer.
The flat-rate codes (no allowance applied)
BR — Basic Rate
Every pound from this source taxed at 20%. No personal allowance applied. Standard for second jobs where the main job already uses the allowance. Wrong if it's on your only income source. Read more about BR →
D0 — Higher Rate (40%)
Every pound from this source taxed at 40%. Standard for second incomes when total annual earnings already exceed £50,270 from the main source. Read more about D0 →
D1 — Additional Rate (45%)
Every pound from this source taxed at 45%. Standard for second incomes when total annual earnings already exceed £125,140 from the main source. Read more about D1 →
NT — No tax
No Income Tax deducted at all. Rare. Reasons: non-residence, certain expatriate arrangements, or specific exempt categories. Read more about NT →
The K code (negative allowance)
A K-prefix code is the inverse of a standard code: instead of subtracting your allowance from income before applying tax, HMRC adds extra taxable income to your pay. Common causes:
- Benefits in kind (company car, private medical) exceeding your personal allowance
- Owing tax from a previous year, collected via current-year PAYE
- Multiple income sources where HMRC needs to claw back collected allowances
A K475 code means £4,750 of additional taxable income is added to your earnings during the year. Read more about K codes →
The Scottish (S) and Welsh (C) prefixes
A letter prefix indicates the tax bands of your tax residence:
- S — Scottish taxpayer. Scotland's income tax bands apply (different rates and thresholds). Personal allowance unchanged at £12,570.
- C — Welsh taxpayer. Currently the same bands as rUK (England + NI), but separate code lets the Welsh Senedd vary if it chooses.
Example: S1257L = Scottish taxpayer with standard personal allowance.
Tax residence is determined by where you live, not where you work. Cross-border commuters use their home address tax code.
The emergency suffixes (W1, M1, X)
A W1, M1 or X at the end of the code signals emergency basis — each pay period is calculated standalone rather than cumulatively:
- W1 — weekly emergency (1/52 of allowance each week)
- M1 — monthly emergency (1/12 of allowance each month)
- X — generic non-cumulative
Common causes: starting a new job without a P45, gap in HMRC's data, complex tax position needing manual review. Usually resolves automatically within a few pay periods. Read more about emergency tax →
How PAYE applies a tax code
For a normal cumulative code (no emergency suffix):
- HMRC sends your code to your employer at year start (or whenever it changes)
- Each pay period, your employer's payroll system looks at your year-to-date earnings
- It calculates the correct Income Tax for the year-to-date based on your code's allowance and the bands above it
- The deduction in this period = total tax due year-to-date minus tax already paid year-to-date
This cumulative method is why early-year months often look unusual — your year-to-date catches up to where it should be.
For emergency basis (W1/M1/X), each period is treated standalone with no year-to-date catch-up.
Worked example — 1257L on £50,000
Annual position:
- Gross: £50,000
- Personal allowance: £12,570 (tax-free)
- Taxable income: £37,430
- All within the basic rate band (up to £50,270)
- Income Tax: £37,430 × 20% = £7,486
- National Insurance: separate calculation
Monthly: - Gross: £4,167 - Tax: ~£624 - NI: ~£250 - Take-home: ~£3,293
See the £50,000 after tax page → for the full breakdown.
Worked example — BR on £20,000
Annual position:
- Gross: £20,000
- Personal allowance: £0 (BR ignores it)
- Taxable income: £20,000
- All taxed at basic rate
- Income Tax: £20,000 × 20% = £4,000
Compare to 1257L on £20,000: - Personal allowance applied: £20,000 − £12,570 = £7,430 taxable - Income Tax: £7,430 × 20% = £1,486
BR costs this person £2,514 extra per year compared to 1257L. If BR is wrong on their only job, they're overpaying significantly and should fix it.
When your code looks wrong
Six common reasons your code might be wrong:
- Started a new job without a P45 — HMRC defaults to emergency code
- Recent benefit in kind change — gained or lost company car / healthcare
- Recently applied for Marriage Allowance — switching from L to N or M
- HMRC owed-tax recovery — code lowered to collect previous-year underpayment
- Second job double-counted — both jobs trying to apply allowance
- Region change — moved to or from Scotland / Wales
Read the full troubleshooting guide →
How to check and fix your code
- Your HMRC Personal Tax Account — shows your current code with the calculation behind it. Free, online.
- The HMRC mobile app — same data as the Personal Tax Account
- Your P2 Notice of Coding letter — sent when HMRC changes your code
- Call HMRC on 0300 200 3300 — for changes that can't be self-serviced
Most simple code issues resolve within 2-6 weeks once raised. PAYE will refund overpaid tax automatically through your next payslip cycle.
Tax codes and pension contributions
Pension contributions interact with your tax code:
- Salary sacrifice: reduces your gross income before tax → code doesn't change, but the lower gross means less tax
- Relief at source: contribution comes out of net pay; tax relief is applied to the pension. Code doesn't change.
- Net pay arrangement: contribution comes out of pre-tax pay; effectively your code's allowance is applied to a smaller gross
Read more about how pension contributions affect take-home →
In short
UK tax codes are a compact instruction set for PAYE. The number is your annual personal allowance (divided by 10); the letters and prefixes describe your circumstances. 1257L is the standard 2026/27 code for most employees; variations signal specific situations (Marriage Allowance, second jobs, benefits in kind, region, emergency basis). The tax code checker → decodes any code instantly, and the spoke pages linked above go deeper on each variant.