The 1242L tax code gives you a tax-free Personal Allowance of £12,420 for the year, which is £150 less than the £12,570 that the standard 1257L code provides.1GOV.UK. Understanding Your Employees Tax Codes – Overview HMRC has trimmed your allowance for a specific reason: usually a small workplace benefit, an underpayment carried forward from a previous year, or another minor adjustment. The letter L is the standard suffix, so nothing unusual is going on with your category — it’s the number that’s telling the story.
What the Number and Letter Actually Mean
Every PAYE code has a number and a letter. The number is your annual tax-free income with the last digit removed, so 1242 means £12,420. Your employer’s payroll software uses that figure to work out how much Income Tax to deduct from each payslip.2GOV.UK. Tax Codes – What Your Tax Code Means
The L confirms you’re entitled to the standard category of Personal Allowance. It tells your employer you haven’t transferred any of your allowance to a spouse and don’t have an unusual adjustment that would require a different letter.3GOV.UK. Understanding Your Employees Tax Codes – What the Letters Mean L is by far the most common suffix, but it doesn’t automatically mean you have the full standard allowance. It just means the standard rules apply to whatever allowance HMRC has calculated for you.
Why Yours Is £150 Lower Than 1257L
The standard Personal Allowance for the 2025/26 tax year is £12,570, which corresponds to 1257L.4GOV.UK. Income Tax Rates and Personal Allowances A 1242L code means HMRC has reduced that figure by exactly £150. The reduction isn’t a mistake and it doesn’t mean you’ve done anything wrong, but it does mean a deduction is baked into your tax calculation.
The usual reasons HMRC lowers a code include:5GOV.UK. Tax Codes – Why Your Tax Code Might Change
- A workplace benefit like a company car, private medical insurance, or another taxable perk reported by your employer. A benefit valued at £150 a year would move your code from 1257L to exactly 1242L.
- Underpaid tax from a previous year. If you owed a small amount, HMRC often collects it by shrinking your allowance rather than sending a bill.
- State Pension or other taxable state benefits paid without tax deducted, offset against your employment income.
- The High Income Child Benefit Charge, if your income exceeds £60,000 and your household claims Child Benefit.
- Untaxed savings interest above your Personal Savings Allowance.
A £150 reduction is small, so in most cases it points to a single low-value benefit or a modest underpayment adjustment rather than several deductions stacked together.
What 1242L Costs You in Take-Home Pay
Payroll spreads your £12,420 allowance evenly across the year. If you’re paid monthly, roughly £1,035 of each month’s pay is tax-free. Weekly earners get about £239 tax-free per week. Anything above that prorated amount is taxed at the applicable rate.
For 2025/26, the rates above your Personal Allowance are:4GOV.UK. Income Tax Rates and Personal Allowances
- Basic rate of 20% on taxable income from £12,571 to £50,270
- Higher rate of 40% on taxable income from £50,271 to £125,140
- Additional rate of 45% on taxable income above £125,140
Because 1242L gives you £150 less tax-free income than 1257L, a basic-rate taxpayer pays an extra £30 across the full year, or about £2.50 a month. That is exactly why many people never notice it. If the deduction turns out to be wrong, though, the same small figure repeats year after year until someone catches it.
Most codes run on a cumulative basis, meaning payroll tracks your total pay and tax from the start of the tax year and self-corrects each pay period. A pay rise or a bonus one month is balanced against what you’ve already paid, so the deductions even out.6GOV.UK. HMRC PAYE Manual – PAYE11090
How to Find Out Which Deduction Applies to You
HMRC sends a P2 coding notice whenever they change your code, and it lists every deduction that has been applied. If you kept the letter, that’s your answer. If you didn’t, your Personal Tax Account on GOV.UK or the HMRC app will show the same breakdown, along with how the number was calculated.7GOV.UK. Check Your Income Tax for the Current Year
Your most recent payslip confirms the code currently being used by your employer. Your P60, issued after the end of each tax year, summarises the full year’s pay and tax.8GOV.UK. Your P45, P60 and P11D Form Between the P2 and the online account, you should be able to identify the £150 deduction without needing to call anyone.
How to Correct It if the Deduction Looks Wrong
You can update your details through the Personal Tax Account or the HMRC app. Common corrections include telling HMRC you no longer receive a benefit, updating income estimates, or reporting a change in circumstances. Once HMRC processes the update, they issue a revised P2 to you and send new instructions to your employer electronically. Your employer then applies the new code in the next payroll run.
The Income Tax helpline is the alternative if you’d rather speak to someone. Have your National Insurance number, payslip, and P60 ready before you call.
What Happens if the Wrong Code Ran All Year
After each tax year ends on 5 April, HMRC reviews PAYE records and sends a P800 calculation to anyone who paid too much or too little. These go out between June and March of the following year.9GOV.UK. Tax Overpayments and Underpayments
If you overpaid because 1242L should have been 1257L, the P800 will explain how to claim the refund. You can also claim through your Personal Tax Account. The time limit is four years from the end of the tax year in which the overpayment happened.
If you underpaid, HMRC usually collects small amounts under £3,000 by adjusting the following year’s code rather than asking for a lump sum.10GOV.UK. Tax Overpayments and Underpayments – If You Owe Tax That coded-in underpayment is itself one of the more common reasons for a code lower than 1257L, so if you had a 1257L code last year and a 1242L code now, an underpayment adjustment is a strong candidate for the cause.
If You Earn Close to £100,000
The standard £12,570 Personal Allowance starts to shrink once adjusted net income exceeds £100,000. HMRC removes £1 of allowance for every £2 you earn above that threshold, and the allowance disappears entirely at £125,140.4GOV.UK. Income Tax Rates and Personal Allowances Someone earning £105,000 would lose £2,500 of allowance and end up on 1007L, not something as high as 1242L. If your income is anywhere near £100,000 and your code is 1242L, either the taper hasn’t been applied or your adjusted net income is being reduced by pension contributions or Gift Aid. It’s worth confirming which.
What Changes in April 2027
One of the most common reasons for a small allowance reduction is a benefit reported on a P11D form, with HMRC then adjusting your code to collect the tax. From April 2027, employers will be required to “payroll” most benefits instead, adding the taxable value directly to your pay each period so tax is deducted in real time.11GOV.UK. Technical Note – Mandating the Reporting of Benefits in Kind and Expenses Through Payroll Software – An Update The change was originally set for April 2026 but has been pushed back a year.
Once payrolling takes effect, HMRC will automatically remove benefit deductions from tax codes. If your 1242L exists because of a payrolled benefit, expect your code to move back toward 1257L after the transition, with the tax collected through your payslip instead. Employment-related loans and accommodation are temporarily exempt, so those benefits may still show up as a code reduction beyond April 2027.