An emergency tax code is not a penalty rate and it is not permanent. It is a code that tells payroll to treat this period as if it were every period of the year, with no cumulative history behind it, because your employer does not yet have your previous pay and tax details. GOV.UK names the three markers: W1 where you are paid weekly, M1 where you are paid monthly, X where pay dates vary. What it costs depends on which code carries the marker, and on a first payslip in a new job the answer is often nothing at all, which is why so many people search for this after the second one.
Find the marker on the payslip
Look at the tax code and its suffix. 1257L W1, 1257L M1 or a code ending X is the emergency form of the standard code; BR taxes everything at the basic rate with no allowance; 0T taxes everything with no allowance and runs through the bands. The marker is the whole difference between an emergency code and its ordinary twin, and the code itself is printed on every payslip.
Work out what the period alone would pay
An emergency 1257L still gives an allowance, but only that period's share of it: £1,047.50 in a month, £241.73 in a week, and nothing carried forward. On a £2,500 monthly gross that produces £290.50 of Income Tax, which is the same as the cumulative code would take on a steady salary. The difference only shows when your pay across the year is uneven, or when you started part way through and have unused allowance sitting behind you.
Price the codes that give no allowance
BR is the expensive one on a main job: every pound taxed at 20% with no allowance, so a £2,500 month pays £500 rather than £290.50, and £209.50 a month too much. 0T is worse again on higher pay, because it runs the bands with no allowance at all. On a SECOND job BR is often correct, since the allowance is usually already used by the first, which is why the same code can be right or wrong depending on what else you are paid.
Get the code corrected, and the money back
HMRC updates the code once it has your details from the new and previous employer, which GOV.UK says can take up to 35 days from starting the job. Give your new employer the P45 from your last one, or complete the starter checklist if you have no P45. Once a cumulative code arrives, the payroll recalculates the year to date and the over-payment comes back in that month's pay rather than as a separate refund.
Know the case that does not correct itself
If the emergency code was triggered by a company benefit or the State Pension rather than a new job, GOV.UK says you keep it until the end of the tax year and move to a non-emergency code in the new one. The over-payment is then settled after the year ends rather than through the payroll. It is also the case where the code is worth checking against the benefit's actual value, because a coded estimate that is too high costs real money every month until April.
Questions people ask about emergency tax calculator
What is an emergency tax code?
A code ending W1, M1 or X. It tells payroll to tax the period on its own, as if you were paid that amount every period of the year, instead of recalculating the whole year to date.
How much does emergency tax cost me?
On an emergency 1257L with a steady salary, often nothing: the month gets a twelfth of the allowance either way. On BR it is 20% of everything with no allowance, which is £209.50 a month too much on a £2,500 gross.
How do I get off an emergency tax code?
Give your employer your P45, or fill in the starter checklist if you do not have one. HMRC issues a cumulative code once it has the details from both employers, which can take up to 35 days from starting the job.
Will I get the overpaid tax back?
Yes. On a new job it comes back through the payroll in the month the cumulative code arrives. Where the emergency code came from a benefit or the State Pension, it is settled after the tax year ends instead.