A 743L tax code means HMRC has set your tax-free personal allowance at £7,430 for the year rather than the standard £12,570. The number, multiplied by ten, is your allowance; the L confirms you qualify for a version of the standard personal allowance.1GOV.UK. Tax Codes Something specific has stripped £5,140 out of your allowance, and at the 20% basic rate that costs you roughly £1,028 more in tax over the year, or about £86 a month compared with the usual 1257L code.
What the 743 and the L Actually Tell You
Every UK tax code is a number and a letter. The number is your annual tax-free allowance in shorthand: add a zero to get the real figure. The letter tells your employer’s payroll which rules to apply. L is the most common suffix and simply means the standard personal allowance applies to you.1GOV.UK. Tax Codes
The standard personal allowance is £12,570 and has been frozen at that level since 2021/22, with legislation keeping it there until at least 5 April 2031.2GOV.UK. Income Tax: Maintaining the Personal Allowance So unless HMRC has a reason to adjust your allowance, 1257L is what you should be seeing. Any code lower than that is telling you a story, and 743L is one you can decode.
Why Your Code Might Be 743L
A £5,140 reduction doesn’t happen by accident. HMRC lowers your personal allowance in response to specific circumstances, and in most cases one or a combination of the following is behind it.
A Company Car or Other Benefit in Kind
Workplace perks with monetary value are taxable. A company car, private medical insurance, an employer-paid gym membership: each has a taxable value, which HMRC subtracts from your personal allowance so the tax comes out of your regular pay rather than as a separate bill. Your employer reports these values to HMRC on a P11D after the end of each tax year.3GOV.UK. Expenses and Benefits for Employers: Reporting and Paying
Company cars are the most common cause of large code reductions because the taxable amount depends on the car’s list price and CO2 emissions, and a high-emission vehicle can easily produce a benefit worth several thousand pounds. If you recently took a company car or moved to one with higher emissions, that alone could account for a drop from 1257L to 743L.
A Tax Underpayment Being Collected Through Your Code
If you underpaid income tax in a previous year, HMRC often recovers it by reducing your current allowance rather than sending a bill. This is called coding out. On your coding notice it appears as a specific line item, and it spreads the repayment across the year in small deductions from each paycheck.
HMRC can only code out underpayments up to £2,999.99 this way. Anything at or above £3,000 has to be collected through Self Assessment or a direct payment.4GOV.UK. PAYE Manual – PAYE12070 There is also a safeguard: HMRC shouldn’t code out an amount that would more than double the tax taken from your pay. Your P60 from the year in question shows total pay and tax and is the easiest place to sanity-check whether an underpayment really occurred.5GOV.UK. Your P45, P60 and P11D Form: P60
You Transferred Part of Your Allowance to a Spouse
Marriage Allowance lets a lower-earning spouse or civil partner transfer £1,260 of their personal allowance to their partner, saving the recipient up to £252 a year.6GOV.UK. Marriage Allowance If you’re the one transferring, your own allowance drops by £1,260. On its own that wouldn’t produce 743L, but combined with other adjustments it can be part of the total.
A State Pension You’re Also Receiving
The state pension is taxable but arrives without any tax deducted. If you receive both a state pension and income from a job or private pension, HMRC accounts for the pension by cutting the code applied to your other income. Someone receiving £11,500 in state pension would have that subtracted from £12,570, leaving £1,070 of tax-free income against their wages, so their code would land near 107L.
The state pension by itself is unlikely to give you exactly 743L, but paired with a small benefit in kind or a modest coded-out underpayment, the numbers can land there.
The High-Income Taper
Once your adjusted net income passes £100,000, your personal allowance shrinks by £1 for every £2 over the threshold, disappearing entirely at £125,140.7GOV.UK. Income Tax Rates and Personal Allowances To reach 743L through the taper alone, your income would need to be around £110,280: half of the £10,280 above £100,000 is the £5,140 reduction that leaves £7,430. This catches out people whose pay has risen recently, because HMRC estimates the current year’s allowance based on the previous year’s earnings.
How to See Exactly Why Your Code Is 743L
The quickest way to find out which of the above applies to you is HMRC’s “Check your Income Tax” service. Sign in at GOV.UK using a Government Gateway ID or GOV.UK One Login account.8GOV.UK. HMRC Online Services: Sign in or Set Up an Account The service shows your current code, a line-by-line breakdown of every adjustment feeding into it, your estimated income from each job or pension, and the total tax HMRC expects you to pay this year.9GOV.UK. Check Your Income Tax for the Current Year
That breakdown is where most people find the real answer. Benefits in kind are listed by type, underpayments show the year and amount, and marriage allowance transfers are labelled. Before you review it, pull out any P11D forms and your latest P60 so you can cross-check what HMRC has on file against what actually happened. Discrepancies usually come from benefits that ended partway through the year, a job change reported late, or estimated income figures that turned out wrong. HMRC’s mobile app lets you view your code as well, though it doesn’t currently support submitting changes.10GOV.UK. Download the HMRC App
Fixing a Code That’s Wrong
If the breakdown shows something that isn’t right, say a company car you handed back months ago or a coded-out underpayment that doesn’t match your records, you can submit a correction through the same online service. It lets you update your estimated income, report changes to benefits, or flag a specific adjustment as incorrect.9GOV.UK. Check Your Income Tax for the Current Year If you’d rather speak to someone, HMRC’s income tax helpline handles the same changes. Have your National Insurance number and any supporting documents ready.
Once the update is processed, HMRC issues a P2 Notice of Coding explaining the new code line by line, and sends the code electronically to your employer’s payroll.11GOV.UK. PAYE Manual – PAYE11030 – P2 Notice of Coding HMRC aims to complete updates within 15 working days. If you’re paid monthly, expect the new code on your next payslip or the one after; weekly-paid workers usually see it within about three pay periods.12GOV.UK. Tax Codes: If You Think Your Tax Code Is Wrong
Getting Back Tax You’ve Already Overpaid
When HMRC corrects your code, they also check whether the old code took too much tax. If it did, they instruct your employer or pension provider to refund the difference through your pay, and you’ll typically see a larger net amount on the payslip where the correction lands.13GOV.UK. Tax Codes: If You’ve Paid Too Much or Too Little Tax
If the overpayment sits in a tax year that has already ended, the process is slower. HMRC reconciles records after 5 April using final pay data from employers, and if that shows you overpaid, they write to you explaining how to claim. This can take several months, so flagging a wrong code as soon as you notice it is worth the small effort.
If You Actually Owe the Tax
Sometimes a 743L code is correct and reflects real tax you owe. In that case, timing matters. As of January 2026, HMRC’s late payment interest rate is 7.75%, set at the Bank of England base rate plus 4%.14GOV.UK. HMRC Interest Rates for Late and Early Payments Interest runs from the date the tax was originally due, not from when HMRC discovers the shortfall. If you have an underpayment large enough that it can’t be coded out (£3,000 or more), paying it directly is cheaper than letting it wait for a Self Assessment bill to catch up with you.