Emergency Tax Calculator, 2026/27

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.

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.