It is the letter that explains your tax code in plain figures — and the single best document for catching an error before it costs you money.
The PAYE coding notice is the document most people throw away and later wish they had read. It is HMRC showing its working: every allowance added and every deduction taken to arrive at the tax code your employer uses. Read it once a year and you will rarely be caught out by an unexpected tax bill.
A coding notice walks through the arithmetic behind your tax code. It starts with your tax-free allowances and subtracts anything that should reduce them:
The same notice is often called a notice of coding; the two terms describe the identical document. You can read more on the notice of coding page.
Suppose Daniel earns £45,000 and has a company car with a taxable benefit of £4,800. His 2025/26 coding notice would show:
| Line | Amount |
|---|---|
| Personal Allowance | £12,570 |
| Less: car benefit | −£4,800 |
| Net tax-free amount | £7,770 |
| Tax code (£7,770 ÷ 10, drop the last digit) | 777L |
So instead of the standard 1257L, Daniel's code is 777L, meaning less of his pay is tax-free because his car benefit uses up part of his allowance. If the car benefit on the notice were wrong, say it listed a vehicle he had returned, he would be paying too much tax until it was corrected. Confirm the live code at any time by choosing to check your tax code.
A coding notice is the earliest warning you get that something is off. Because it explains the reasoning rather than just stating the code, it lets you spot the specific item that is wrong: a benefit you no longer have, an estimated figure that is too high, an other-income amount HMRC has guessed, or an old underpayment that has already been settled. Catching it here, before the code feeds into payroll, prevents months of incorrect deductions and the hassle of reclaiming them later.
A particularly common trap is HMRC carrying forward an estimated company benefit or untaxed income from a previous year. If your circumstances have changed, that estimate can be stale, leaving you on the wrong code for months. The notice is also where adjustments for things like the High Income Child Benefit Charge or a state pension appear, so it is the document that ties together everything affecting your PAYE tax. Scottish taxpayers will see an S prefix (S1257L) and Welsh taxpayers a C prefix (C1257L) on their notice, reflecting which nation's rates apply, even though Welsh rates currently match those in England.
A coding notice is HMRC explaining itself in advance. Ignore it and you accept its assumptions; read it and you can correct them before they cost you.
If you are purely self-employed, you will not normally receive a coding notice, because a tax code only governs income taxed through PAYE. Your tax is settled annually through Self Assessment, and from April 2026 through Making Tax Digital quarterly updates feeding into a final declaration. However, if you also have employment or a pension alongside your self-employment, those sources have a tax code and you will receive a coding notice for them.
There is one situation where the two worlds meet directly. If your Self Assessment bill is under £3,000 and you have a PAYE income, HMRC can collect that balance by adjusting your tax code rather than asking for a separate payment, a process it calls coding out. When it does, the adjustment appears on your coding notice, so even sole traders with a side job or a pension should read any notice they receive rather than assuming it is irrelevant to them.
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