Emergency Tax Calculator, 2026/27
Starting a new job without a P45 often means being placed on an emergency tax code, which can overtax your first few payslips. Enter your monthly salary to compare emergency tax against your normal tax code and estimate any refund due once it is corrected.
The emergency tax calculator runs on the rates and thresholds HMRC has published for the 2026/27 tax year, so the figures you see reflect the position your company is actually filing on rather than a historic set of bands. Change any input and the result recalculates immediately, with no sign-up and nothing sent anywhere.
If you are a director of a UK limited company, use it as a first look before a decision rather than as the decision itself. 1257L Week 1/Month 1 gives one month's worth of personal allowance and tax bands each pay period with no carry forward, which usually undertaxes or roughly matches the normal code depending on when in the year you start. Real company positions bring in other income, reliefs, group structures and prior year adjustments that a single page of inputs cannot see, which is why the workings are written out below under personal & self assessment tax. Read those, then check the numbers against your own accounts, and speak to us if anything looks materially different from what you expected.
Last reviewed 12 September 2026 for the 2026/27 tax year. Reviewed by Waqas Sagar, Member of ICAEW, Fellow of ACCA, Fellow of AAT.
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Result, 2026/27
Tax under the emergency code this month
Tax under your normal cumulative code
Extra tax paid this month
Refund once HMRC issues the correct code
Usually repaid automatically through payrollIllustration only, figures are based on the rates you have selected and the information entered. Please check your own position with us before acting.
Estimates for the 2026/27 tax year using published GOV.UK rates. Switch between 2026/27 and 2025/26 above.
How this is calculated
When you start a new job without a P45, or your employer has incomplete information, HMRC's default is to place you on an emergency tax code, most commonly 1257L on a Week 1 or Month 1 basis, which gives you one month's worth of allowance and bands each pay period rather than the normal cumulative calculation.
Some employers instead use BR, taxing every pound at the basic rate with no personal allowance at all, or 0T, which applies the full progressive bands but with no personal allowance, both of which typically result in more tax being deducted than under a normal tax code.
The calculator compares your emergency code tax for the month against what a normal cumulative 1257L code would produce for the same salary, spread evenly across the year, to show the likely overpayment.
Why emergency tax happens
The most common trigger is starting a new job without bringing a P45 from your previous employer, or starting your first ever job and not completing a starter checklist correctly, both of which leave HMRC and your new employer without the information needed to set the right code immediately.
Other triggers include starting a second job, receiving certain benefits, or having a gap in employment where your tax code was not updated in time.
Getting it fixed
In most cases, once your new employer receives the correct information from HMRC, usually within a few weeks, your tax code is corrected and any overpaid tax from earlier in the year is automatically refunded through your next payslip.
If it is not corrected before the end of the tax year, or you have left the job, you can claim the overpaid tax back directly from HMRC, usually by completing an online form once you have all your pay and tax details for the year.
What this means for your company
Treat the result as a planning figure for the 2026/27 tax year. If it changes what you were about to do, take a director's salary, a dividend, a large asset purchase or a filing decision, check it against your own accounts first. We can review the position with you and confirm the tax treatment before you commit.
Frequently asked questions
Will I definitely get emergency tax back?
In most cases yes, since once HMRC issues the correct tax code your employer's payroll software automatically recalculates your tax cumulatively and refunds any overpayment through your next payslip, usually within a pay period or two.
How long does emergency tax usually last?
It typically lasts until HMRC has the information needed to issue your correct code, which is often just one or two pay periods if you provide a P45 or complete a starter checklist promptly when you begin the job.
What is the difference between 1257L M1 and BR?
1257L Month 1 gives you one month's personal allowance and bands with no cumulative catch-up, while BR taxes everything at 20% with no personal allowance at all, so BR is usually the more aggressive of the two.
What if my tax code is still wrong at the end of the year?
You can contact HMRC directly or claim through your Personal Tax Account, and any overpaid tax for the year will be refunded once your final pay and tax figures for the year are reconciled.
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