How PAYE actually works
PAYE is HMRC system for collecting income tax + NI through your employer. Each pay period:
1. Your employer reports your YTD gross pay + tax-deductible benefits to HMRC.
2. HMRC tells employer your "tax code" - typically 1257L = GBP 12,570 annual personal allowance.
3. Employer calculates tax due on YTD pay using cumulative bracket math:
- First GBP 12,570 of annual pay: 0%
- GBP 12,571 - GBP 50,270: 20%
- GBP 50,271 - GBP 125,140: 40%
- Above GBP 125,140: 45%
4. Employer deducts the difference between YTD tax owed and YTD tax already deducted.
| National Insurance (NI) | Tax code structure |
|---|---|
| Class 1 employee: 8% on earnings GBP 12,570 to GBP 50,270 (rate cut from 12% in January 2024); 2% above | 1257L: standard, GBP 12,570 allowance, "L" indicates no special circumstances |
| Employer also pays NI separately (not deducted from your gross): 15% on most earnings | 1100L: reduced allowance, e.g. for owed back tax in prior year |
| NI not part of PAYE tax code but uses same earnings basis | K-prefix (e.g. K500): negative allowance (you owe tax on benefits exceeding allowance) |
| BR (basic rate): 20% on all pay (no allowance) - typically for second job | |
| 0T: 0% allowance applied (used for new starters before P45) | |
| NT: no tax (special cases - foreign service, etc.) | |
| W1/M1 emergency code: non-cumulative, used when employer cannot verify |
If your tax code is wrong: contact HMRC online or call 0300 200 3300. They issue updated tax code to employer.
Top 5 mistakes ranked
1. Wrong tax code applied after job change
You changed jobs mid-year. Old employer issued P45. New employer should use P45 to set tax code. If P45 was lost or delayed:
- Code BR (20% on everything) often applied as default
- Result: under-using your annual GBP 12,570 personal allowance
- Common over-withholding: GBP 2,500+ depending on months mis-coded
Fix: contact HMRC, get correct cumulative tax code, employer recalculates and refunds.
2. Missing higher-rate pension tax relief
You pay GBP 5,000 into SIPP. HMRC automatically adds GBP 1,000 (20% basic rate). But you are higher-rate (40%) taxpayer - the extra 20% (GBP 1,000) requires SELF ASSESSMENT claim. Many higher earners miss this.
Fix: File annual Self Assessment and claim extra relief.
3. Skipping salary sacrifice when available
Salary sacrifice = lower salary in exchange for employer contributions (pension, EV car, bike scheme).
- Saves income tax + employee NI + employer NI
- For 40% taxpayer with full pension match: net cost of GBP 1 pension is about 52p
- vs ordinary pension SIPP (relief at source) where 40% taxpayer cost is 60p
Fix: ask HR if salary sacrifice available. If yes, use it for pension, EV lease, bike-to-work, childcare.
4. Not claiming Marriage Allowance
If one spouse earns under GBP 12,570 (or just over the personal allowance) and other is basic-rate (20%): you can transfer 10% of your personal allowance (GBP 1,260) to your spouse.
- Spouse gets GBP 252 less tax per year
- Can backdate up to 4 years (one-time refund)
- Apply at gov.uk/marriage-allowance
Fix: lower earner applies; one-time decision lasts indefinitely.
5. Personal Allowance taper at GBP 100K
For every GBP 2 of adjusted income above GBP 100,000, personal allowance reduces by GBP 1. Lost entirely at GBP 125,140.
- Effective marginal tax rate between GBP 100K and GBP 125K: 60% (40% standard + 20% lost allowance)
- Salary sacrifice into pension is the only escape
Fix: at GBP 100K+ income, prioritize pension contributions (salary sacrifice) to drop AGI back under GBP 100K and restore allowance.
| Band | Income range | Income tax | NI rate |
|---|---|---|---|
| Personal allowance | GBP 0 - 12,570 | 0% | 0% |
| Basic rate | GBP 12,571 - 50,270 | 20% | 8% (Class 1) |
| Higher rate | GBP 50,271 - 125,140 | 40% | 2% |
| Additional rate | Above GBP 125,140 | 45% | 2% |
| Taper zone (100-125K) | GBP 100K-125,140 | Effective 60% | 2% |
Ranks 6-10
6. Treating bonus as 40% tax when really marginal
Bonus tax is calculated AT YOUR MARGINAL RATE in the month received.
- If your regular monthly salary is GBP 4,000 (annualized GBP 48K, basic rate 20%): bonus of GBP 5,000 in that month is mostly at 40% because annualized monthly pay exceeds GBP 50,270 threshold
- BUT - PAYE is cumulative. The over-deduction in the bonus month is recovered in subsequent months as cumulative tax aligns to actual annual liability.
Fix: do not panic about bonus month tax. Year-end balances out via cumulative PAYE.
7. Confused emergency tax codes (BR, 0T, NT)
BR: basic rate 20% on all earnings, no allowance. Used for second job (since main job uses the allowance).
0T: 0% allowance, marginal rates on all (used for new starters before P45).
NT: no tax (very rare; foreign assignment, students with limited UK income).
When seeing W1/M1 in code: emergency code (non-cumulative). Resolve by providing P45 to employer.
Fix: confirm tax code matches your situation. Contact HMRC if unsure.
8. Missing professional subscription / uniform tax relief
Professional fees on the HMRC approved list (RCN, BMA, GMC, ACCA, CIMA, etc.): claim back tax on annual subscription via Self Assessment or Form P87.
Uniform / work clothing maintenance: GBP 60 flat rate annual deduction (nurses, mechanics, security, etc.).
Working from home: GBP 6/week tax-free for 2025-26 if working from home is requirement of role (not discretionary).
Fix: file Form P87 for prior 4 years to claim.
9. Forgetting Self Assessment after side hustle
Did you sell on Etsy? Drive Uber? Have rental property? Make crypto gains? If side income over GBP 1,000 (trading allowance): you must file Self Assessment by January 31 following the tax year.
Fix: keep income records. File Self Assessment annually. Pay any additional tax due.
10. Wrong tax code rolling forward
HMRC updates tax codes annually based on prior tax year data. Errors compound:
- Got bonus in 2023 that pushed you into higher rate
- HMRC assumed bonus would repeat
- Underdeducted allowance for 2024
- Discovered in P800 reconciliation 18 months later
Fix: review tax code each April. Submit "Tell HMRC about change in income" online if circumstances changed.
Tax codes decoded + how to fix
Annual P60: year-end statement of total gross pay + tax + NI for tax year (April 6 - April 5). Your employer issues by May 31.
P45: leaver statement when you change jobs. Three parts: Part 1 stays with old employer, Parts 2+3 go with you to new employer.
P11D: company benefits statement (company car, healthcare, dental). Tax due on these "benefits in kind."
P800: end-of-year reconciliation HMRC sends if you over- or under-paid via PAYE.
Monthly payslips show
- Gross pay
- Tax deducted (line for income tax)
- NI deducted (separate line)
- Pension contribution (if applicable)
- Salary sacrifice (if applicable)
- Net pay (take-home)
Review payslip monthly. Catch errors early.
How to fix wrong tax code:
1. Sign in to your Personal Tax Account at gov.uk/personal-tax-account
2. Click "Tax code" - see current code + recent changes
3. If wrong, click "Tell HMRC about a change to my income"
4. Provide details (e.g. "starting new job," "salary changed," "lost benefit")
5. HMRC issues updated code; employer applies next month
6. If overpaid: refunded via lower deductions in remaining year, or refund by P800 after year-end
Real-time PAYE: from 2024 reforms, HMRC receives weekly pay data from employers. Easier to spot errors early. Use your Personal Tax Account to monitor.
Common knock-on PAYE issues
- Second job: typically gets BR code (20% on entire second-job income, no allowance). Correct if first job uses full allowance. Wrong if first job is under allowance.
- Director loans / dividends: not paid through PAYE. Self Assessment.
- P11D benefits: company car at GBP 5,000 list value: 24% petrol benefit charge = GBP 1,200 added to taxable income. Often missed.
- EV / hybrid: 2% benefit charge in 2025-26 (rising 1% per year through 2028). Huge tax saving vs petrol/diesel.
- Healthcare: employer-provided BUPA = GBP 1,000-3,000 P11D benefit. Tax on this benefit is small (GBP 200-600 for basic rate) but easy to overlook.
- Living accommodation: if employer provides, fair rental value added to taxable income.
- Childcare vouchers: closing scheme; new Tax-Free Childcare scheme available - 20% government top-up on up to GBP 10,000 childcare costs.
- Cycle to Work: salary sacrifice for bike + accessories. Combined NI + tax saving: 30-40% of bike cost.
- EV salary sacrifice: 2025-26 huge tax win, leasing an EV through company saves 40-50% on monthly cost for higher-rate taxpayers.
- Pension salary sacrifice: most efficient way to save into pension if available. Saves both employer + employee NI on top of income tax relief.
If in doubt: call HMRC 0300 200 3300, or chat via your Personal Tax Account online.
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