The 1124L tax code means HMRC has set your tax-free Personal Allowance at £11,240 for the year instead of the standard £12,570. That £1,330 reduction is deliberate: HMRC is usually collecting underpaid tax from an earlier year, accounting for a taxable employment benefit like a company car, or adjusting for other income. Your employer uses the code the same way as any other PAYE code, withholding income tax from each payslip based on the reduced allowance.
What the Number and Letter Actually Mean
A PAYE code has two parts. The number, multiplied by ten, is your tax-free amount for the year. So 1124 × 10 = £11,240.1GOV.UK. Understanding Your Employees’ Tax Codes – What the Numbers Mean Compare that with the far more common 1257L, which gives you the full £12,570 Personal Allowance.2GOV.UK. Understanding Your Employees’ Tax Codes
The letter L simply confirms you qualify for a Personal Allowance on standard grounds.3GOV.UK. Tax Codes – What Your Tax Code Means It’s the number that tells the real story. A figure below 1257 means something is reducing what you can earn tax-free.
Why Your Allowance Is £1,330 Lower Than Standard
Most employees are on 1257L. If you’re on 1124L, HMRC has a specific reason for shaving £1,330 off your allowance. The usual explanations fall into a few groups.
Underpaid Tax From a Previous Year
If you underpaid tax in an earlier year — through a wrong code, overlapping jobs, or untaxed income — HMRC can collect the shortfall by lowering your current allowance, spreading the repayment across the year rather than sending you a bill. This happens automatically for underpayments below £3,000 where you filed on time.4GOV.UK. Pay Your Self Assessment Tax Bill – Through Your Tax Code A £1,330 reduction at the 20% basic rate collects exactly £266 of extra tax over the year, so that’s likely what you owed.
Taxable Employment Benefits
Perks like a company car, private medical insurance, or similar benefits count as taxable income. Instead of billing you separately, HMRC reduces your allowance so the tax is collected through your payslip.5GOV.UK. Tax Codes – Why Your Tax Code Might Change If the taxable value of your benefits works out to £1,330, that alone would move you from 1257L to 1124L.
Marriage Allowance Plus a Small Adjustment
Transferring £1,260 of your allowance to a spouse through Marriage Allowance reduces yours to £11,310 and produces a code ending in N, not L.6GOV.UK. Marriage Allowance – How It Works So a straight Marriage Allowance transfer isn’t the answer here. But if a minor benefit or underpayment sits alongside other adjustments, the combined figure could land on 1124L with an L suffix. If your code letter is L, benefits or underpayments are the more likely cause.
A Second Job or Pension
With two sources of PAYE income, HMRC normally gives one employer the full allowance and puts the other on a BR or 0T code. Sometimes, though, HMRC splits the allowance between the two or adjusts one code to reflect your estimated total income, producing an unusual number like 1124.5GOV.UK. Tax Codes – Why Your Tax Code Might Change
What 1124L Costs You in Take-Home Pay
Your employer’s payroll spreads the £11,240 allowance evenly across the year, sheltering around £937 of each month’s pay from tax. Everything above that gets taxed at the usual rates: 20% up to £50,270 of total income, 40% up to £125,140, and 45% above.7GOV.UK. Income Tax Rates and Personal Allowances
On a £30,000 salary, 1257L leaves £17,430 taxable and a bill of about £3,486. Under 1124L, taxable income rises to £18,760 and the bill climbs to roughly £3,752. That’s about £266 more tax over the year, or roughly £22 less in your monthly pay. Not enormous, but worth pinning down, especially if the reduction shouldn’t be there.
How to Check Whether the Code Is Right
Checking your code is your responsibility, not HMRC’s.8GOV.UK. Tax Codes – Overview You’ll find the current one on your payslip, in the HMRC app, or through the “Check your Income Tax” service on GOV.UK.9GOV.UK. Check Your Income Tax for the Current Year
The online service is the most useful because it breaks down how HMRC arrived at 1124L: your Personal Allowance, anything reducing it, and the resulting tax-free figure. If HMRC sent you a Notice of Coding (a P2) by post or through your online account, that document shows the same arithmetic — the allowance, any deductions, and the amount you can earn at each tax band.10GOV.UK. PAYE Manual – PAYE11030
Before contacting HMRC, gather your National Insurance number (it’s on payslips, your P60, or benefit letters), your recent payslips, and your latest P60.11GOV.UK. Find Your National Insurance Number If you get taxable benefits from your employer, note their value. Then compare what HMRC assumes against what’s actually happening.
Correcting the Code If It’s Wrong
If the breakdown doesn’t match your situation — you no longer have the company car, or HMRC is collecting an underpayment you’ve already paid off — use the “Check your Income Tax” service to update your income estimates, report changes to benefits, or flag anything else affecting the code.9GOV.UK. Check Your Income Tax for the Current Year
You can also call the Income Tax helpline on 0300 200 3300, Monday to Friday, 8am to 6pm.12GOV.UK. Income Tax – Enquiries Have your National Insurance number to hand.
Once HMRC processes the change, they issue an updated Notice of Coding and send your employer an electronic notification. The corrected code usually appears on your payslip within one or two pay cycles.
Getting Money Back If You’ve Overpaid
If a wrong code has led you to overpay, HMRC may send a P800 tax calculation letter after the tax year ends, showing the amount owed to you. These letters go out between June and March.13GOV.UK. Tax Overpayments and Underpayments If yours confirms an overpayment, you can claim online or wait for a cheque.
If you think you’ve overpaid but no P800 has arrived, you can start a claim yourself through GOV.UK. HMRC often catches the error automatically, but not always, and delays mean the money stays with the government longer than it should.
Interest on Underpayments You Don’t Fix
If HMRC later finds you’ve underpaid, interest runs on the outstanding amount at 7.75%, calculated as the Bank of England base rate plus 4%, and moves whenever the base rate moves.14GOV.UK. HMRC Interest Rates for Late and Early Payments Whether a penalty is added depends on how the underpayment happened. An honest mistake caught by HMRC usually attracts no penalty beyond interest. Failing to take reasonable care — for example, ignoring a Notice of Coding you knew was wrong — can bring a penalty of 0% to 30% of the additional tax.15GOV.UK. Penalties – An Overview for Agents and Advisers If you spot something wrong with 1124L, it’s cheaper to raise it than to wait.
One Boundary Worth Noting
If you’ve just started a new job and the figures on your payslip look off, check that you’re actually on 1124L rather than an emergency code. Emergency codes appear when a new employer doesn’t yet have your previous pay and tax details, and they’re marked with a W1, M1, or X suffix, or sometimes “NONCUM” on the payslip.16GOV.UK. Tax Codes – Emergency Tax Codes A plain 1124L with no suffix is a normal cumulative code and behaves like any other permanent code.