UK Emergency Tax Code Overpayment Refund 2026 Calculator
A UK emergency tax code (1257L W1/M1, BR, 0T, D0, D1) ignores your year-to-date pay and personal allowance, so you usually overpay tax in the first pay period. This 2026/27 calculator shows how much you have overpaid and how to claim it back from HMRC.
| Gross pay this period | — |
| Emergency code used | — |
| Correct cumulative code | — |
| Tax under emergency code (period) | — |
| Tax under correct code (period) | — |
| Year-to-date gross (estimated) | — |
| Overpayment this period | — |
| Total estimated overpayment YTD | — |
An emergency tax code is what HMRC tells your employer or pension provider to use when they do not yet know your full tax history — most commonly when you start a new job without a P45, take a first job after study, or draw from a pension for the first time. Because the code does not look at your year-to-date pay or accumulated personal allowance, you usually overpay in the first few pay periods.
What Each Emergency Code Means
1257L W1/M1 — the most common 2026/27 emergency code. It gives you your full personal allowance (£12,570) but treats each pay period in isolation (Week 1 or Month 1 basis) instead of accumulating allowance across the year. BR taxes everything at the 20% basic rate with no allowance. 0T uses no personal allowance but does respect the bands (20% / 40% / 45%). D0 taxes everything at 40%, and D1 at 45% — both usually appear on a second job or pension where your allowance is fully used elsewhere.
How the Overpayment Adds Up
The 1257L W1/M1 code splits the £12,570 allowance evenly across pay periods (£1,047.50/month or £241.73/week). That works for steady earners but breaks if you started mid-year — months of unused allowance are simply lost. If you start work in month 6, the cumulative 1257L code would let you use 6 × £1,047.50 = £6,285 of unused allowance straight away, but the W1/M1 code only gives you the current month's £1,047.50. On a £4,000 monthly salary that overcollects roughly £1,257 in tax in the first month alone.
How To Claim Your Refund
HMRC reconciles your tax automatically at the end of the tax year (5 April) via the PAYE annual reconciliation and sends a P800 tax calculation letter. If you are owed money, the letter tells you how to claim — most refunds now flow through your Personal Tax Account (gov.uk/personal-tax-account) within 5 working days of claiming. To get the refund during the tax year, give HMRC a copy of your P45 (or complete a new starter checklist) — your employer will then apply the correct cumulative code and refund the overpayment in your next payslip. For pension drawdowns, you can also use form P55 (small lump sum), P53Z (whole pension), or P50Z (stopped work).
Common Emergency Tax Mistakes
(1) Waiting for the P800 — you can claim during the year by submitting P45 / starter checklist; do not leave £1,000s sitting with HMRC. (2) Wrong starter declaration — picking statement C on the new starter checklist (other income / pension) forces the BR code; pick A or B when applicable. (3) Ignoring a K code — K codes are not emergency codes; they reflect a real underpayment or company benefits and should be left alone. (4) Refund scams — HMRC will never text or email a refund link. Always log into your Personal Tax Account directly at gov.uk.
Sources: HMRC / HM Revenue & Customs (gov.uk/tax-codes), PAYE Income Tax Manual, Personal Tax Account (gov.uk/personal-tax-account). Last updated May 2026 for the 2026/27 tax year.