What does tax code 400L mean?

Tax code 400L means HMRC has told this employer or pension provider to give you £4,000 of tax-free personal allowance against this PAYE source for 2026/27, rather than the standard £12,570 used on code 1257L. The "L" suffix means you are entitled to the basic personal allowance — the number 400 means £4,000 of it has been allocated here. Above that figure, PAYE is calculated using the normal UK bands.

Why has HMRC given me tax code 400L?

The most common reasons are: (1) you have two or more PAYE sources and HMRC has split your £12,570 personal allowance across them — £4,000 here, the balance elsewhere; (2) HMRC has reduced your allowance to recover underpaid tax from a prior year or untaxed income (state pension, savings interest, taxable benefits); (3) a marriage allowance transfer has reduced your allowance; or (4) you have a benefit in kind (company car, private medical) coded against your allowance. Your HMRC coding notice (P2) should explain which it is.

Is tax code 400L wrong?

Not necessarily. 400L is a valid HMRC tax code. It is "wrong" for you only if the reason behind the reduced allowance no longer applies — for example you have left the second job, the underpayment has cleared, the benefit in kind has ended, or the marriage allowance transfer has been cancelled. Check your P2 coding notice on your HMRC personal tax account and, if the reason is out of date, contact HMRC to update it.

How much extra tax will 400L cost me vs 1257L?

Going from 1257L to 400L removes £8,570 of personal allowance (£12,570 − £4,000). At the 20% basic rate that is roughly £1,714 a year of extra PAYE, or about £142.83 a month. If the lost allowance is being used at a higher PAYE source instead, the net effect across both jobs may be close to nil — what matters is the total, not any single code.

How do I get tax code 400L changed?

Tax codes are set by HMRC, not by your employer. Sign in to your HMRC personal tax account, check your latest P2 coding notice, and use the "Tell HMRC about a change" service or call HMRC PAYE on 0300 200 3300 to update the underlying reason — for example to remove a benefit in kind that has ended, or to redistribute allowance between jobs. Once HMRC re-issues the code, your employer applies it from the next pay period.

Educational guidance only — not regulated tax, financial or payroll advice. Verify with HMRC or your payroll team before acting.

UK · Tax codes · 400L

Tax code 400L — what it means on your UK payslip

If your latest payslip shows tax code 400L, HMRC has told your employer to give you £4,000 of tax-free personal allowance from this job for 2026/27, not the standard £12,570 implied by tax code 1257L. The “L” means you still qualify for the basic personal allowance; the “400” means only part of that allowance has been allocated here. The rest is usually sat against another PAYE source, or has been removed to collect tax on something else.

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How “400L” is built

HMRC tax codes use a simple convention. The number is the tax-free personal allowance for the year divided by 10. The letter at the end describes which scheme of allowances or restrictions applies.

400 × £10 = £4,000. That is the slice of your personal allowance attached to this PAYE source for 2026/27.
L — the standard letter for “entitled to the basic personal allowance”. Different letters (BR, 0T, D0, D1, K, M, N, NT, S, C) signal different rules, see every UK tax-code letter explained.
Under 1257L is unusual. On a standalone job with no other PAYE source, no untaxed income, no benefits in kind and no marriage-allowance transfer, the default code is 1257L, meaning the full £12,570 of personal allowance for 2026/27.

Common reasons HMRC issues a 400L code

Several scenarios can reduce your personal allowance against a specific PAYE source. The most common reasons HMRC quotes in coding notices (form P2) are below, your own P2 will spell out which one applies to you.

Split allowance across two or more PAYE jobs: You have more than one employment or pension at the same time. HMRC has decided to give £4,000 of personal allowance against this source and the remaining £8,570 against another source. Whichever job is your main one normally keeps the larger share. The total across all sources should still equal the standard £12,570.
Untaxed income elsewhere: You receive income that PAYE cannot reach directly, for example State Pension, a private rental, savings interest above the personal savings allowance, or dividends above the dividend allowance. HMRC may use a reduced code on your main PAYE source to recover the tax expected on that other income.
Recent HMRC adjustment for an earlier underpayment: A previous year ended with an underpayment of tax, often picked up during a P800 reconciliation. HMRC may reduce your allowance in the current year so the underpayment is collected gradually through payroll rather than as a one-off bill.
Marriage allowance transfer: You have transferred £1,260 of personal allowance to a spouse or civil partner under marriage allowance. Your code letter on a marriage-allowance reduction is normally "N" (transferring out) or "M" (receiving), but in some split-allowance cases the residual figure can still surface as a low "L" number on a secondary source.
Benefits in kind coded against allowance: Taxable benefits in kind, company car, private medical insurance, accommodation, gym membership, are often collected by reducing your tax code. The cash-equivalent of the benefit is subtracted from your allowance for the year, which can pull the code well below 1257L.

Worked example — £30,000 gross on 400L vs 1257L

Same employee, same £30,000 gross salary, England / Wales / Northern Ireland. The 2026/27 PAYE arithmetic for each code is:

Step	1257L	400L
Gross pay	£30,000	£30,000
Personal allowance against this source	£12,570	£4,000
Taxable pay	£17,430	£26,000
PAYE at 20%	£3,486	£5,200
Extra PAYE on 400L vs 1257L	—	£1,714 / year (≈£142.83 / month)

That extra £1,714 of PAYE is not necessarily a tax rise overall. If the “missing” £8,570 of allowance has been moved to a second job, you save tax there in roughly equal measure. The net effect across all your PAYE sources should match the total tax due on your total income. If you only have one PAYE source and the reduction is collecting an underpayment or untaxed income, the higher figure is real, but the money is going to HMRC to settle a known liability.

What to ask HMRC if 400L looks wrong

Tax codes are set by HMRC, not by your employer. Payroll cannot change the code on its own, it just applies whatever HMRC has sent. The fastest fix is to update HMRC directly.

Find your P2 coding notice. Sign in to your HMRC personal tax account. The P2 lists each PAYE source, the allowance attached to each, and the reason for any reduction.
Check whether the reason is still true. Did you leave the second job? Has the benefit in kind ended? Was the underpayment from a prior year already collected? Has your spouse cancelled the marriage allowance transfer?
Update HMRC. Use the “Tell HMRC about a change” service inside the personal tax account, or call HMRC PAYE on 0300 200 3300. Quote your National Insurance number, the employer or pension provider in question, and what has changed.
Wait for the re-issued code. HMRC sends a fresh code to your employer electronically. Once applied, PAYE adjusts automatically, overpaid tax in the same tax year normally refunds through your next payslip.

If you believe the code is wrong but cannot work out why, the PayslipIQ wrong-tax-code checker walks through the most common patterns and flags ones that usually need an HMRC update.

Frequently asked questions

What does tax code 400L mean?: Tax code 400L means HMRC has told this employer or pension provider to give you £4,000 of tax-free personal allowance against this PAYE source for 2026/27, rather than the standard £12,570 used on code 1257L. The "L" suffix means you are entitled to the basic personal allowance, the number 400 means £4,000 of it has been allocated here. Above that figure, PAYE is calculated using the normal UK bands.
Why has HMRC given me tax code 400L?: The most common reasons are: (1) you have two or more PAYE sources and HMRC has split your £12,570 personal allowance across them, £4,000 here, the balance elsewhere; (2) HMRC has reduced your allowance to recover underpaid tax from a prior year or untaxed income (state pension, savings interest, taxable benefits); (3) a marriage allowance transfer has reduced your allowance; or (4) you have a benefit in kind (company car, private medical) coded against your allowance. Your HMRC coding notice (P2) should explain which it is.
Is tax code 400L wrong?: Not necessarily. 400L is a valid HMRC tax code. It is "wrong" for you only if the reason behind the reduced allowance no longer applies — for example you have left the second job, the underpayment has cleared, the benefit in kind has ended, or the marriage allowance transfer has been cancelled. Check your P2 coding notice on your HMRC personal tax account and, if the reason is out of date, contact HMRC to update it.
How much extra tax will 400L cost me vs 1257L?: Going from 1257L to 400L removes £8,570 of personal allowance (£12,570 − £4,000). At the 20% basic rate that is roughly £1,714 a year of extra PAYE, or about £142.83 a month. If the lost allowance is being used at a higher PAYE source instead, the net effect across both jobs may be close to nil, what matters is the total, not any single code.
How do I get tax code 400L changed?: Tax codes are set by HMRC, not by your employer. Sign in to your HMRC personal tax account, check your latest P2 coding notice, and use the "Tell HMRC about a change" service or call HMRC PAYE on 0300 200 3300 to update the underlying reason, for example to remove a benefit in kind that has ended, or to redistribute allowance between jobs. Once HMRC re-issues the code, your employer applies it from the next pay period.

Every UK tax code, explained one page at a time
The tax-code index — 1257L, BR, 0T, D0, D1, K, M1, NT, S, C and the per-number variants like 400L.
Wrong tax code checker
A guided check for the most common “is this code right for me?” patterns, including reduced-allowance codes.
UK payroll & payslip hub
All PayslipIQ UK guides plus the free payslip check.

Last reviewed

Last reviewed: 16 May 2026

Next review: 6 April 2027

Reviewed each tax year and sooner if HMRC changes the personal allowance or the L-suffix code rules.

Educational guidance only — not regulated tax, financial or payroll advice. Always verify with HMRC or your payroll team before acting. To run a real check, the wrong-tax-code checker is the place to begin.