1084L Tax Code: Allowance Deduction, £100k Taper, and Tax Due

The 1084L tax code means HMRC has told your employer to give you £10,840 of tax-free pay this year, which is £1,730 below the standard £12,570 personal allowance sitting behind the default 1257L code. That gap is not random. HMRC has subtracted something specific from your allowance, and the reason will be spelled out on your PAYE coding notice (the P2). Until you know which adjustment created the shortfall, you can’t tell whether the code is right.

What the Number and Letter Actually Say

A PAYE tax code is a number plus a letter. Drop the final digit of your allowance and you get the number: £10,840 becomes 1084. Multiply the code number by ten to reverse it.¹

The L confirms you’re on the standard personal allowance structure. It’s the most common suffix, and it stays as L even when your allowance has been reduced, as long as the underlying entitlement is the ordinary one rather than a Marriage Allowance transfer, a Scottish or Welsh variant, or another special case.²

Why £1,730 Has Been Taken Off Your Allowance

The standard personal allowance has been frozen at £12,570 since the 2021–22 tax year and remains there through 2026–27. Your code shows that £1,730 has been carved out of that figure, and the P2 coding notice will list the exact items HMRC used to reach that number.³

The usual culprits are:

A taxable work benefit such as a company car, private medical insurance, or another perk. HMRC estimates its cash value and lowers your allowance by that amount so the tax comes out of your regular pay.
Unpaid tax from an earlier year. Rather than demanding a lump sum, HMRC often collects it by shrinking this year’s allowance. A £500 underpayment reduces the allowance by £500 and pulls in roughly £100 of extra basic-rate tax across the year.
Untaxed income such as a state pension. If money is reaching you without tax deducted at source, HMRC may recover the tax due on it by trimming the code applied to your wages.
A Marriage Allowance transfer of £1,260 to a spouse or civil partner. This one usually gives you an N suffix rather than L, so it’s less likely to be the sole cause here.⁴

HMRC often stacks more than one adjustment. A £1,200 company car benefit plus a £530 underpayment from last year adds up to exactly £1,730. That’s why reading the P2 line by line is worth the few minutes it takes.

The £100,000 Taper Lands Right on This Code

There’s one other reason 1084L shows up, and it’s specific enough to check first if you’re a higher earner. Once your adjusted net income passes £100,000, the personal allowance drops by £1 for every £2 above that threshold, disappearing entirely at £125,140. Someone with adjusted net income of £103,460 loses £1,730 of allowance, leaving £10,840. That is the 1084L figure exactly.¹

If your income is in this range, the taper alone may explain the code and no benefits or underpayments need to be involved. A pay rise or bonus that nudges you just over £100,000 can trigger this, and the combined effect of losing allowance while paying 40% on the excess makes the marginal cost of that extra income steeper than it first looks.

How Much Tax You Pay on 1084L

With 1084L, the first £10,840 you earn in the year is tax-free. Anything above that is taxed at the standard rates for England, Wales, and Northern Ireland:¹

20% basic rate on income from £10,841 to £50,270
40% higher rate on income from £50,271 to £125,140
45% additional rate on income above £125,140

On £30,000 of earnings, 1084L means 20% tax on £19,160, so £3,832 for the year. The same salary on 1257L would be taxed on £17,430, giving £3,486. The £346 difference works out to around £29 more tax a month.

Scotland has its own rates and bands. If you work in Scotland, your code would carry an S prefix, and the rates above the allowance would differ from the ones above.

Watch for W1 or M1 Next to the Code

Most codes, including 1084L, run cumulatively. Payroll tracks your total pay and tax from 6 April onwards and adjusts each payslip so the year-to-date figures come out right. Overpay in one month and the next month’s deduction goes down to compensate.⁵

If your code reads 1084L W1 or 1084L M1, it’s operating on a non-cumulative or “emergency” basis. Each pay period is calculated in isolation, ignoring what came before. This avoids sudden refunds or heavy deductions but can leave the year-end total slightly off. HMRC normally shifts you back to a cumulative code once your full employment details reach them.⁶

How to Check the Breakdown

Sign in to your Personal Tax Account on gov.uk to see exactly what HMRC has plugged into your code: which allowances are included, which deductions have been applied, and what income figure they’re working from. Anything wrong can be corrected through the same service.⁷⁸

Have a few documents open while you check. Your P60 shows total pay and tax deducted for the year to 5 April and is the reference for whether the right tax was actually collected.⁹ Your P11D lists the taxable benefits your employer has reported, which you can compare against the benefit deductions in your code.¹⁰ Recent payslips confirm the code being applied and the tax coming out each period.

If you’ve just started a new job, HMRC advises waiting 35 days for the new employment details to reach them before querying the code.⁷

If you’d rather not use the online service, HMRC’s income tax helpline is 0300 200 3300, Monday to Friday, 8am to 6pm. A digital assistant on the HMRC website can also handle simple queries and pass you to an adviser.¹¹ When HMRC agrees a change is needed, a fresh P2 goes to you and your employer, and payroll applies the new code from the next pay period, or within a couple of weeks for weekly-paid staff.³

If the Code Was Wrong and You Overpaid or Underpaid

Once HMRC has the full picture and confirms you’ve paid too much, they instruct your employer or pension provider to refund the overpayment through your regular pay. Monthly-paid employees usually see it on the next payslip or the one after. Weekly-paid employees typically get it within three pay periods.¹²

If you’ve changed jobs and HMRC doesn’t yet hold your details, the refund has to wait. Handing your P45 from the previous employer to the new one speeds this up. Otherwise HMRC receives the employer data after 5 April, reviews what you’ve paid, and writes if anything was off.¹²

Underpayments run the other way. HMRC usually collects the shortfall by adjusting next year’s code, which is how a lot of people end up on something like 1084L to begin with. For larger amounts, HMRC may contact you directly to arrange payment.

1
GOV.UK. Income Tax Rates and Personal Allowances
2
GOV.UK. What Your Tax Code Means
3
GOV.UK. P2 Tax Coding Notice
4
GOV.UK. Marriage Allowance: How It Works
5
GOV.UK. PAYE Manual – PAYE11090
6
GOV.UK. Rates and Thresholds for Employers 2026 to 2027
7
GOV.UK. If You Think Your Tax Code Is Wrong
8
GOV.UK. Personal Tax Account: Sign In or Set Up
9
GOV.UK. Payroll: Annual Reporting and Tasks – Give Employees a P60
10
GOV.UK. Expenses and Benefits for Employers: Reporting and Paying
11
GOV.UK. Income Tax: Enquiries
12
GOV.UK. Tax Codes: If You’ve Paid Too Much or Too Little Tax