C0T is the Welsh version of 0T. You receive no personal allowance, so income is taxed through all Welsh bands from the first pound — often a temporary emergency code.
Zero Personal Allowance, progressive Welsh tax bands from the first pound, and a C prefix confirming you are a Welsh taxpayer. That is the C0T tax code. Unlike CBR (which charges a flat 20%), C0T runs your entire income through all three Welsh rate bands: 20%, 40%, and 45%. This means higher earners on C0T pay significantly more than they would on a flat-rate code. C0T is the Welsh equivalent of 0T, and it is often a temporary emergency code, though it can also be permanent for very high earners.
Both C0T and CBR remove your Personal Allowance. The critical difference is how income tax is calculated.
CBR: flat rate Every pound taxed at 20%, regardless of how much you earn from that source. If you earn £60,000 on a CBR code, all £60,000 is taxed at 20% = £12,000.
C0T: progressive Welsh bands Income is taxed through the full Welsh band structure. The first £37,700 at 20%, the next £87,440 (up to £125,140) at 40%, and everything above £125,140 at 45%.
Here is the difference on £60,000 of income:
| Code | Calculation | Tax due |
|---|---|---|
| CBR | £60,000 at 20% | £12,000 |
| C0T | £37,700 at 20% + £22,300 at 40% | £16,460 |
| Difference | £4,460 more on C0T |
This matters because C0T can produce a much higher tax bill than CBR on the same income. If HMRC has assigned C0T when you should be on CBR (or vice versa), the financial impact is substantial.
There are four main reasons HMRC assigns C0T. Some are temporary, some are permanent, and each requires a different response.
1. New job without a P45 or starter checklist (emergency code). This is the most common reason. When you start a new job in Wales and your employer does not have your P45 or a completed starter checklist, HMRC may assign C0T as a temporary emergency code until they receive the information they need. In this scenario, C0T is usually combined with W1 or M1 (non-cumulative basis), appearing as C0T W1 or C0T M1 on your payslip.
2. Your entire Personal Allowance is allocated elsewhere. If you have multiple income sources and your full £12,570 allowance has been assigned to another employer or pension provider, the remaining sources may receive C0T. This is similar to CBR, but HMRC uses C0T when it wants progressive band taxation applied rather than a flat rate.
3. Your income exceeds £125,140 (allowance fully tapered). The Personal Allowance tapers by £1 for every £2 of income above £100,000. At £125,140, the allowance reaches zero. If your income is at or above this level, C0T may be your permanent code. At this point, every pound is taxed at the higher or additional rate.
4. HMRC has incomplete information about your circumstances. If HMRC cannot determine your correct allowance due to missing data, conflicting employer reports, or unresolved queries, they may issue C0T as a safe default that prevents under-collection of tax.
If C0T is wrong and you should have C1257L, the cost depends on your income level:
| Annual income | Tax on C0T | Tax on C1257L | Annual overpayment | Monthly overpayment |
|---|---|---|---|---|
| £20,000 | £4,000 | £1,486 | £2,514 | £210 |
| £35,000 | £7,000 | £4,486 | £2,514 | £210 |
| £50,000 | £11,432 | £7,486 | £3,946 | £329 |
| £60,000 | £15,432 | £11,432 | £4,000 | £333 |
At incomes above £50,270, the C0T overpayment is worse than CBR because C0T pushes income into the 40% band sooner. At a £50,000 salary, being on C0T incorrectly costs you nearly £4,000 per year.
C0T is correct if:
C0T is probably wrong if:
The fix depends on why you have C0T in the first place.
If it is an emergency code at a new job:
If HMRC records are wrong:
If your allowance is genuinely zero (income above £125,140):
C0T is correct in this case. No fix is needed. However, verify that HMRC's estimate of your income is accurate. If they are overestimating your income (perhaps based on a bonus from a previous year that is not recurring), you may be entitled to a higher allowance than zero.
Yes. Any tax overpaid while on an incorrect C0T code is refundable.
During the current tax year: Once HMRC issues a corrected cumulative code, your employer recalculates your tax from 6 April. The overpayment is refunded through your wages, usually in the next pay period after the code change. If the overpayment is large (several months on C0T), expect a noticeably larger net pay for that month.
After the tax year ends: HMRC issues a P800 tax calculation showing any over- or underpayment. You can view this in your Personal Tax Account. Overpayments are refunded either directly to your bank (if you set up a repayment) or by cheque.
For previous years: You can reclaim overpaid tax for up to four prior tax years by contacting HMRC or submitting a Self Assessment return.
Waiting too long to act. Every month on an incorrect C0T code costs hundreds of pounds. A £35,000 earner overpays £210 per month. Over six months, that is £1,260 you could have in your pocket instead of sitting with HMRC.
Confusing C0T with CBR. They are not the same. CBR is a flat 20%. C0T applies progressive Welsh bands. On higher incomes, C0T costs significantly more than CBR. If you are on C0T but your situation calls for CBR (second job, basic rate Welsh taxpayer), you are paying too much.
Not providing a P45 to a new employer. This is the most preventable cause of emergency C0T codes. Keep your P45 safe when you leave a job and hand it to your new employer on your first day.
Assuming C0T M1 or C0T W1 will fix itself. It often does, but not always. If you are still on a non-cumulative C0T code after three months, contact HMRC. Do not assume the system will self-correct.
Not checking whether the C prefix is correct. If you have recently moved out of Wales, you should be on 0T, not C0T. While the tax calculation is identical for 2025/26 (Welsh rates match England), having the wrong prefix means HMRC's records are inaccurate. If Wales changes its rates in a future year, the wrong prefix could result in the wrong rates being applied.
Related tax codes: Welsh tax codes | CBR tax code | 0T tax code
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