Firefighter Tax Code Explained: 1257L and Emergency Codes

What a tax code is and who sets it

Your tax code is a short instruction that your employer's payroll uses to calculate Income Tax on each payslip. It is set by HMRC, not by your fire and rescue service, and it reflects the tax-free amount you are entitled to for the year, less any income HMRC knows about that has not yet been taxed (such as a taxable benefit or a small pension). GOV.UK says the code is used by your employer or pension provider to work out how much Income Tax to take.

The service simply applies whatever code HMRC sends. That means a wrong code is almost never a payroll error; it usually follows from information HMRC holds: a previous job, an old benefit, a second income, an underpayment from an earlier year or a change such as Marriage Allowance. You can see it on your payslip, on a Tax Code Notice letter, in your online personal tax account or in the HMRC app.

Codes are set for each tax year, which runs from 6 April to 5 April. In 2026/27 the Personal Allowance remains £12,570, so the standard code is unchanged from recent years. That figure is used for the calculations in the site's pay calculator, which you can use to see the code in action.

Decoding 1257L and the other letters

HMRC builds a code from your Personal Allowance of £12,570, subtracts any untaxed income and deductions such as company benefits or the High Income Child Benefit Charge, then replaces the last digit with a letter. The example on GOV.UK: a £1,570 medical insurance benefit reduces the allowance to £11,000 and gives code 1100L. So the number is the tax-free allowance with the last digit dropped, and the letter says what type of allowance you have.

L is the standard Personal Allowance. M means you have received Marriage Allowance from your partner. N means you have given Marriage Allowance away. T means your code includes other calculations. BR taxes all your income at the basic rate, and D0 / D1 at the higher / additional rate; they usually appear on second jobs or pensions. 0T gives no allowance, typically when HMRC lacks information. K means untaxed income exceeds your allowance, so the code adds to your taxable pay.

The extra 8 in 1265L, for example, is what an £80 uniform flat rate expense produces: allowance rises by £80, and dividing by 10 adds 8 to the number. See firefighter tax relief for how to claim it.

Emergency tax codes: W1, M1 and X

An emergency code is issued when your employer does not have enough information from HMRC or a P45. GOV.UK says emergency codes end in W1 (weekly), M1 (monthly) or X, and that when you are on one your tax is calculated only on your current payment, as if you would get the same amount in every pay period for the rest of the year. This is called a non-cumulative basis and can cause over- or under-payment.

For a firefighter this most often arises when you transfer between services, join from another job, or come back from a career break. If your first payslip shows 1257L M1, you are probably being taxed correctly for that month if your pay is steady, but it can go wrong if a month includes a large one-off payment such as back pay, a pay-award backdate, or several months of overtime. In that month the code treats the payment as if you would earn it every month, so you could be pushed into the higher rate on paper.

GOV.UK says HMRC typically takes up to 35 days to update your code once it has information from both employers. If your code remains an emergency one after that, contact HMRC. Any tax overpaid is refunded when the code is corrected. Our guide to firefighter back pay explains how backdated pay awards are paid and taxed.

How overtime is taxed (it is not 'taxed at 40%')

A common belief is that overtime is 'taxed harder'. It is not. On a cumulative code (the normal case) payroll adds your gross pay for the year to date, subtracts the free-pay allowance to date, and applies the tax bands to what is left. Overtime simply adds to gross pay in the month you are paid, so it is taxed at whichever band your total pay so far sits in.

Worked example: competent firefighter on £40,358, 12.59% pension, overtime £1,000 in one month. Overtime is normally not pensionable, so pension stays the same. Taxable pay for the year is £35,276.93 after pension, well below £50,270, so the extra £1,000 is taxed at 20%: £200 tax, plus 8% National Insurance: £80. Take-home from the £1,000 is £720. With a Plan 2 student loan there would be a further 9% (£90) if that month's total pay exceeds the loan threshold, leaving £630.

Higher-band example: Station Manager Competent B at £57,402. Taxable pay after 14.09% pension is £49,314.06, which is £955.94 below the £50,270 higher-rate threshold. £12,000 of overtime therefore takes £955.94 at 20% and £11,044.06 at 40%. Tax on the overtime is £191.19 + £4,417.62 = £4,608.81 (38.4% of the £12,000). NI on the overtime is 2% (£240) because pay is above £50,270. The rest, £7,151.19, is take-home. Estimate your own with the overtime calculator.

Second jobs, on-call pay and BR / D0 codes

If you work as a wholetime firefighter and also do paid work elsewhere, or you are on-call in one service and employed elsewhere, HMRC normally puts your Personal Allowance against your main job and gives the second income a BR code (basic rate on all pay) or a D0 code (higher rate) so that no extra allowance is used. That is normal, not an error.

Worked example: wholetime competent firefighter with £4,000 a year of second-job pay on BR. Tax on the second job is 20% x £4,000 = £800. Because the firefighter's taxable income is £35,276.93 (pension deducted), the second income stays within the basic-rate band, so £800 is correct. If the firefighter's taxable income were above £50,270, the correct tax would be 40% x £4,000 = £1,600, and HMRC would need to collect an extra £800, usually by a K code or Self Assessment. For non-tax rules about outside work see our second job guide.

On-call earnings deserve special care: HMRC's manual on fire officers' allowances lists retaining fees, turn-out fees and attendance fees as taxable extra pay. If your on-call employer is a different service from your full-time one, expect a BR or D0 code on one payslip. Check both codes add up to one Personal Allowance in total, not two. Try the on-call pay calculator for likely earnings.

K codes, underpayments and benefits in kind

A K code is unusual for firefighters but does happen. It means HMRC thinks you have more untaxed income or benefits than your allowance covers, so the number is added to your pay before tax rather than subtracted. Common causes: a large taxable benefit, a previous-year underpayment being collected through your code, or an untaxed income source such as a small state or private pension.

Worked example. A K code of K475 adds £4,750 to taxable pay. On £40,358 with pension deducted (£35,276.93), the code makes the figure taxed £40,026.93 with no allowance at all. That looks harsh, but the code is only right if HMRC's information is right. If the underpayment came from a one-off, it should drop back next year; ask HMRC how the K number was built.

HMRC also limits how much of an underpayment can be collected through your code, and we have not re-verified the exact cap for 2026/27, so treat that as a prompt to ask rather than a promise. If collection is causing hardship, call HMRC and explain.

How to check your code and fix errors

Start with your latest payslip and find the tax code. If it is 1257L (or 1265L with the uniform claim) and there is no W1 / M1 / X, you are on the normal cumulative basis and your tax to date should equal the tax on your pay to date. Next, sign in to your HMRC online account or app: it shows the current-year code and how the allowance was built, including any deductions for benefits.

If something is wrong, use HMRC's service to update the change (for example to add or remove a benefit, tell HMRC about a second job or to claim Marriage Allowance). HMRC will then send a new code to your employer, who applies it from the next payroll. Any overpaid tax comes back through your pay or as a refund, and underpaid tax is collected the same way. Keep a note of the date you told HMRC.

1. Read the tax code and any suffix (W1 / M1 / X) on your latest payslip.
2. Compare with 1257L; explain any difference (benefit, Marriage Allowance, uniform relief).
3. Sign in to your HMRC personal tax account and open the Income Tax section.
4. Update HMRC with any missing income, benefit or job change online.
5. Check your next payslip shows the corrected code and no emergency suffix.
6. If tax was overpaid, confirm the refund arrives; chase HMRC if it does not.

Pay-award backdating, pension and Scotland

Backdated pay awards can produce a strange-looking month: several months of arrears in one payslip. On a cumulative code that is fine, because total tax is worked out on year-to-date pay. If you are on an emergency or non-cumulative basis it can over-tax that month. See firefighter pay rise back pay for how and when arrears are paid after the July 2026 award.

Pension: FPS contributions are taken before tax, so your code applies to pay after pension. Rates and thresholds are in firefighter pension contributions 2026. Your code number does not change because of pension, but taxable pay does. In Scotland the code carries an S prefix (S1257L) and payroll applies Scottish bands; a Welsh taxpayer's code carries a C prefix (C1257L) for Welsh rates, currently the same as rUK.

Once your code and pay are correct, use our pay report or the salary report to see gross-to-net for your rank, and the take-home pay guide for the rank tables.