Emergency Tax Calculator UK 2025/26

Emergency tax calculator UK 2025/26 — see overpayment under codes 1257L M1/W1, BR, 0T or D0. Estimate your refund, learn

Quick answer: Emergency tax codes (1257L M1/W1, BR, 0T) over-deduct tax when starting a new job without a P45. Most refunds are £300–£800 automatically corrected within 1–2 pay periods. Submit P45 or call HMRC 0300 200 3300 to fix.
Mustafa Bilgic
Reviewed by Mustafa Bilgic · UK Calculator Editor ·

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Started a new job and seen huge tax deductions? You're likely on an emergency tax code. This calculator shows how much you've overpaid based on which emergency code you're on, and how to claim it back.

How emergency tax calculator works in 2025/26

HMRC uses an emergency tax code when an employer doesn't have your full income history. The four common emergency codes:

  • 1257L M1/W1 (most common) — applies the full £12,570 allowance but on a non-cumulative basis. Each pay period treated as if it's month 1, ignoring YTD income. Often results in mild over- or under-payment depending on timing.
  • BR — Basic Rate only (20%). Applied to ALL pay with NO personal allowance. Used for second jobs and pensions where allowance is on a different income source.
  • 0T — Zero allowance, but uses full bands (20%/40%/45%). Applied when HMRC doesn't know your tax history at all (no P45, no Starter Checklist).
  • D0 / D1 — Higher rate (40%) or Additional rate (45%) on ALL pay. Used for second jobs of high earners.

How to fix emergency tax:

  1. Give your new employer your P45 from your previous job (or complete the HMRC Starter Checklist if no P45).
  2. HMRC will issue a correct cumulative code (e.g. 1257L) within 4-6 weeks.
  3. Once corrected, your next payslip auto-refunds the overpayment (lower tax that period).
  4. If still wrong after 8 weeks, call HMRC 0300 200 3300 or check your Personal Tax Account.

Worked example: £35,000 on BR code (no allowance)

BR taxes everything at 20% = £7,000 vs correct £4,486. Overpaid £2,514 across the year. Auto-refunded once 1257L is applied.

Gross: £35,000 → Take-home: £26,205.60/year (£2,183.80/month)

Worked example: £50,000 on 0T code

No PA, full bands: £37,700 × 20% + £12,300 × 40% = £12,460 vs correct £7,486. Overpaid £4,974 if uncorrected for full year.

Gross: £50,000 → Take-home: £34,529.40/year (£2,877.45/month)

Worked example: £25,000 on 1257L M1

Same final tax as cumulative (£2,486) but unsmoothed. Over-pay early months, under-pay later. Net overpayment usually £0–£200.

Gross: £25,000 → Take-home: £21,519.60/year (£1,793.30/month)

Frequently asked questions

Why am I on an emergency tax code?
Common reasons: started a new job without P45 (most common), changed jobs mid-year, started receiving a pension, became self-employed alongside PAYE, or HMRC hasn't received your previous employer's P45 details yet.
How long does emergency tax last?
Usually 1–2 months. Once your employer submits your starter info to HMRC and HMRC issues a correct code, the over-deducted tax is automatically refunded through PAYE on your next payslip.
What does M1 or W1 mean on my tax code?
M1 (monthly 1) or W1 (week 1) means your tax is calculated on a non-cumulative basis — each pay period treated independently. The tax-free allowance is split equally across periods (£1,047.50/month) instead of carrying over.
Will I automatically get my emergency tax back?
Usually yes — once HMRC issues a cumulative code, your next payslip recalculates YTD tax and refunds the difference. If you leave the job before correction, file form P50 or wait for end-of-year reconciliation.
How do I claim emergency tax back faster?
Three options: (1) Give your new employer your P45 from your previous job, (2) Complete a Starter Checklist if no P45, (3) Call HMRC on 0300 200 3300 with your NI number ready. Online via Personal Tax Account also works.
Can I be on emergency tax for a whole tax year?
Yes — if you never give P45/Starter Checklist or HMRC never gets correct info. End-of-year reconciliation (P800/Simple Assessment) will refund overpayment via cheque or BACS within 6–12 weeks of tax year end.
Is the 1257L M1 code worse than BR?
Generally 1257L M1 is much better — it gives you the full £12,570 allowance just unsmoothed. BR gives zero allowance, costing you up to £2,514/year (20% × £12,570). 0T is even worse for higher earners as it uses 40%/45% bands.

Official UK Sources

Last reviewed: May 2026 against HMRC 2025/26 rates.

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