Skip to main content
2026/27 Tax Year

Emergency Tax and Refund Checker

Use this when a new job, first payslip, missing P45 or strange code has left you wondering whether HMRC or payroll has taken too much. It compares a common emergency-code outcome with a normal cumulative 1257L position and shows the likely refund route.

Common trigger: emergency tax often appears when payroll does not yet have enough information, especially after a job change. GOV.UK says employers should usually use the starter checklist if a P45 is not available.
By · Reviewed

Your payslip setup

This is a first-pass estimator for the tax side only. National Insurance and payroll timing quirks are intentionally left out.
Estimated overpaid tax so far
£0 Current-code tax on this payslip: £0
Estimated tax on this payslip using the current code£0
Normal cumulative tax due to date on 1257L£0
Tax recorded to date after this payslip£0
Difference versus normal cumulative code£0
Likely statusNo obvious issue
Likely refund routeNo refund path needed
Current-code meaningCurrent code type explained here

What this means

A week 1 or month 1 code ignores earlier pay and tax. That can be harmless for a short period, but if payroll never receives the correct data it can leave you temporarily over or under taxed.

Tax code guide

Sources

Rules and rates checked on 3 October 2026 against GOV.UK: emergency tax codes (W1, M1, X and NONCUM; HMRC usually updates the code within 35 days of a new job starting), HMRC: rates and thresholds for employers 2026 to 2027 (Personal Allowance of £242 a week or £1,048 a month; 20% to £37,700 of taxable pay, 40% to £125,140, 45% above) and GOV.UK: tax overpayments and underpayments (refunds by P800 after the tax year).

Worked examples — see the maths on real numbers

How emergency tax codes work and when refunds happen automatically vs need claiming.

Sam — first job of the tax year starts in August, no P45

New monthly salary£3,500 gross
Tax code applied (no P45)1257L M1 (emergency, monthly)
Months workedAugust to November 2026 (tax months 5 to 8); no other income since 6 April

The maths:

  1. M1 gives one month's allowance each month and ignores April to July
  2. Per month: (£3,500 − £1,048.25) × 20% = £490.35
  3. Tax taken August to November: 4 × £490.35 = £1,961.40
  4. Cumulative 1257L at month 8: allowance to date 8 × £1,048.25 = £8,386; pay to date £14,000; (£14,000 − £8,386) × 20% = £1,122.80
  5. Overpaid by the end of November: £1,961.40 − £1,122.80 = £838.60, which is the April to July allowance (4 × £1,048.25) at 20%

Result: By November Sam has paid about £839 more than a normal code would have taken. GOV.UK says HMRC usually sends the correct code within 35 days of a new job starting; once payroll switches to cumulative 1257L, the next payslip refunds the difference. Left on M1 all year (August to March), he would pay £3,922.80 against a true bill of £3,086 ((£28,000 − £12,570) × 20%), and HMRC would refund the gap after the tax year ends.

Maria — multiple jobs, BR code mistakenly applied to main

Main job£40,000 (code BR)
Side job£8,000 (code 1257L)
Tax year2026/27

The maths:

  1. BR on main job: £40,000 × 20% = £8,000 (no Personal Allowance)
  2. 1257L on side: £8,000 − £8,000 of allowance used = £0
  3. Total tax deducted: £8,000
  4. Correct: combined income £48,000 − £12,570 PA = £35,430 × 20% = £7,086
  5. Over-payment: £914

Result: Maria's codes are swapped — main job should have 1257L (with the bigger allowance), side job should be BR. Ask HMRC to move the allowance to the main job, online through your personal tax account or by phone. Once the new codes reach both payrolls, the main job's cumulative code refunds what it can, and anything left is refunded by P800 after the tax year ends. Always check which job has 1257L.

Figures use 2026/27 UK tax-year rates and thresholds. Always verify against your specific payslip or tax statement before acting.

Editorial accountability
Open Trust Centre →

Pages are checked against the primary sources listed on each page and reviewed by the Editor; corrections are logged in the changelog. Pages are drafted with the help of AI tools (how AI is used). No affiliate revenue. No sponsored content. No paid placements.

Editorial standards Editorial process Corrections policy How we make money The Editor Methodology

UK Tax Drag is an independent publication by Finsolve Consulting Limited, not affiliated with or endorsed by HMRC, GOV.UK or any government body.

How this checker works

This page compares two things: the estimated tax effect of the current code on this payslip, and the cumulative tax due to date if the same pay had instead been processed on a standard 1257L cumulative code for 2026/27.

Sources and practical route

GOV.UK emergency tax codes GOV.UK tax codes overview HMRC PAYE starter checklist guidance GOV.UK claim a tax refund

If the code is genuinely temporary and payroll later receives the correct details, the correction often happens automatically through payroll. If it does not, the refund can instead flow through a Personal Tax Account claim, a P800 reconciliation, or Self Assessment if you already file.