Where all of this comes from

Income tax is charged at the basic rate on an individual’s income up to the basic rate limit

Income tax is charged at Scottish rates on the non-savings income of a Scottish taxpayer.

An individual who makes a claim is entitled to a personal allowance of £12,570 for a tax year if the individual meets the requirements of section 56 (residence etc).

An individual is entitled to a tax reduction for a tax year of the appropriate percentage of the transferable amount

the individual is not, for the tax year, liable to tax at a rate other than the basic rate…

"The appropriate percentage" is the basic rate or default basic rate or, in the case of a Scottish taxpayer or Welsh taxpayer, the Scottish basic rate or Welsh basic rate

"The transferable amount … for the tax year 2016-17 and subsequent tax years, is 10% of the amount of personal allowance specified in section 35(1)". s.55B(5): "If the transferable amount … would otherwise not be a multiple of £10, it is to be rounded up to the nearest amount which is a multiple of £10."

the personal allowance … is reduced for the tax year by the transferable amount

Step 1 Take the basic rate, higher rate or additional rate. Step 2 Deduct 10 percentage points. Step 3 Add the Welsh rate (if any) set by the National Assembly for Wales for that year.

The Inland Revenue must determine the code for use by an employer in respect of an employee for a tax year.

such other adjustments as may be necessary to secure that, so far as possible, the tax in respect of the employee’s income in relation to which the code is determined will be deducted from the relevant payments made during that tax year

"tax tables" means the tax tables prepared by the Board of Inland Revenue under section 685 of ITEPA

UT is any tax not deducted because of the overriding limit when the last relevant payment was made to the employee, and is nil if the payment in question is the first relevant payment to the employee in any tax year

If TT + UT exceeds PT, the employer must deduct the excess from the relevant payment on making the payment.

But … the deduction is not to exceed the overriding limit, subject to 62(6) (notional payments).

An employer must deduct tax in accordance with regulation 27 (the non-cumulative basis) from any relevant payment made to an employee if— (a) the Inland Revenue direct, or (b) these Regulations provide, that the non-cumulative basis is to apply.

On making a relevant payment, the employer must deduct the amount of tax which would have been deductible in accordance with the appropriate tax tables, by reference to the employee’s code, if the payment had been made on the first day of the tax year.

… the deduction is not to exceed the overriding limit, subject to regulation 62(6) (notional payments).

If an employee’s code is the higher rate code the employer must deduct tax at the higher rate, and regulations 22 and 26 (cumulative and non-cumulative basis) do not apply.

If the employee’s code is the additional rate code the employer must deduct tax at the additional rate and regulations 22 and 26 … do not apply.

If the employee’s code is an appropriate Scottish upper rate code the employer must deduct tax at the Scottish upper rate specified in that code and regulations 22 and 26 … do not apply.

If an employee’s code is the nil tax code the employer must not deduct or repay any tax, and so regulation 22 (cumulative basis) does not apply.

"code" means— (a) a combination of letters, numbers or both for use in accordance with the tax tables to establish free pay, additional pay, total free pay to date or total additional pay to date

"K code" means a code which gives rise to additional pay or total additional pay to date.

"S code" means a code which effects deductions of tax at the rates set by a Scottish rate resolution of the Scottish Parliament under section 80C of the Scotland Act 1998.

"C code" means a code which effects deductions of tax at the rates calculated under section 6B of ITA.

the 0T code, which without allowing for personal allowances, effects deductions of tax so that during the tax year the amounts subject to deductions are in accordance with section 10 of ITA … or section 11A of ITA (income charged at Scottish rates)

Starter 19%, basic 20%, intermediate 21%, higher 42%, advanced 45%, top 48% for 2026-27.

"Rates and bands for 2026 to 2027 … Basic rate £12,571 to £50,270 20%; Higher rate £50,271 to £125,140 40%; Additional rate over £125,140 45%." "HMRC will add a 'C' to the start of your tax code so that you pay the right rates."

Basic rate 20%, higher rate 40%, additional rate 45%, for 6 April 2026 to 5 April 2027.

"The emergency tax codes from 6 April 2026 are: 1257L W1, 1257L M1, 1257L X." Wales section: "Basic tax rate 20% Up to £37,700; Higher tax rate 40% From £37,701 to £125,140; Additional tax rate 45% Above £125,140." Scotland section: starter 19%, basic 20%, intermediate 21%, higher 42%, advanced 45%, top 48%.

The "Letters / What they mean" table, retrieved 2026-08-13, listing exactly: 0T, BR, C, C0T, CBR, CD0, CD1, D0, D1, K, L, M, M1, N, NONCUM, NT, S, S0T, SBR, SD0, SD1, SD2, SD3, T, W1, X.

SEARCH_BASIS (2026-08-13): gov.wales/welsh-rates-income-tax returns HTTP 403 to curl and loads in the estate headful Firefox fleet, so the block is a channel property and not an absence. Read through the fleet, the page states "Last updated: 9 March 2022" and its rates section names only the 2023 to 2024 resolution — it states no 2026-27 figure. The site's own search returns "0 results" for both "Welsh rate resolution income tax 2026-27" and "welsh rates of income tax", i.e. it cannot find the very page just read, so the empty search is a broken-search finding and NOT evidence that no publication exists. What IS published, by HMRC, is the operative Welsh rate (see the two GOV.UK cites), and s.6B is inverted against it.