To change a 0T tax code, either give your employer the paperwork they’re missing (a P45 from your last job or a completed starter checklist) or update your income details with HMRC directly, online through the “Check your Income Tax” service or by calling the Income Tax helpline on 0300 200 3300. Whichever route fixes it, HMRC sends your employer a new code and any tax you overpaid on 0T is usually refunded automatically through your next payslip. Under a 0T code, no Personal Allowance is applied to that income, so every pound is taxed at 20%, 40%, or 45% depending on the amount.1GOV.UK. Income Tax Rates and Personal Allowances
Start With Your Employer, Not HMRC
Most 0T codes appear because payroll is missing information about you, and most get fixed at the payroll desk without HMRC ever needing to intervene. If you started a new job recently, hand your employer the P45 from your previous role. It shows your tax code when you left, your earnings for the year so far, and the tax already deducted, which is usually enough for payroll to replace 0T with the correct code.
If you don’t have a P45, ask your employer for a starter checklist and complete it. The checklist asks you to pick one of three statements, and your choice determines the code payroll assigns:
- Statement A: this is your first job since the last 6 April and you haven’t received certain benefits. Your employer applies the full Personal Allowance.
- Statement B: this is your only current job, but you’ve had another since 6 April or received benefits. Your employer applies the Personal Allowance on a week-1/month-1 (non-cumulative) basis.
- Statement C: you have another job or pension. Your employer applies a BR code (basic rate, no Personal Allowance).
Picking the right statement stops 0T from being applied at all. If you’ve already been taxed under 0T for a pay period or two, submitting the checklist late still works. Your employer updates their records and HMRC sends the correct code shortly after.2GOV.UK. Tax Codes – What the Letters Mean
Change It Online Through HMRC
If the paperwork route doesn’t apply, or you want to update HMRC directly, the fastest option is the “Check your Income Tax” online service. Sign in through your Government Gateway account. If you don’t have one, you can create credentials during the process, and you may need to verify your identity with photo ID such as a passport or driving licence.3GOV.UK. Check Your Income Tax for the Current Year
Once you’re in, the service shows your current tax code for each job or pension. You can tell HMRC about a new job, correct your estimated earnings for the year, or update your employer or pension provider details. The system recalculates your code from whatever you enter, and where 0T is wrong, it generates a corrected code and sends it to your employer.
One limitation: if Self Assessment is your only way of paying income tax, this service won’t work for you. Handle it through your Self Assessment return or contact HMRC directly instead.
Change It by Phone
If you’d rather speak to someone, call the Income Tax helpline on 0300 200 3300. It’s open Monday to Friday, 8am to 6pm, and closed on bank holidays.4GOV.UK. Income Tax Enquiries Have your National Insurance number, your employer’s PAYE reference, and an estimate of your total income for the current tax year to hand. The agent will update your records and, if a code change is warranted, trigger it from their end. If you can’t use a standard telephone, Relay UK is available by dialling 18001 before the number.5GOV.UK. Get Help From HMRC If You Need Extra Support – If You Cannot Use a Telephone and Need a Different Way to Contact HMRC
What to Have Ready
Before you contact HMRC or your employer, pull together a few pieces of information. You’ll need your National Insurance number, which appears on any payslip, a P45, a P60, or previous HMRC correspondence.6GOV.UK. Find Your National Insurance Number
You’ll also need your employer’s PAYE reference, which follows the format of three digits, a forward slash, and up to ten letters and numbers (for example, 123/AB456). It appears on your payslip and ensures the corrected code reaches the right payroll department. Finally, estimate your total expected income for the current tax year by adding what you’ve earned so far to what you expect to earn for the rest of it. HMRC compares your estimate against their records, and any gap between the two is usually what triggered the wrong code in the first place.
If you left a job recently, your P45 from that employer is the single most useful document. If the tax year has already ended, a P60 from the former employer serves a similar purpose as the annual record of earnings and tax paid.
When 0T Is Actually Correct
Not every 0T code is a mistake, and in some cases trying to change it will only cause the same code to come back. If you hold more than one job or receive multiple pensions, your full £12,570 Personal Allowance is normally allocated to your main income source, and each additional source gets coded with no allowance. 0T is a standard way to reflect that.
Higher earners also land on 0T legitimately. Your Personal Allowance drops by £1 for every £2 your adjusted net income exceeds £100,000, and once you reach £125,140 the allowance disappears entirely.1GOV.UK. Income Tax Rates and Personal Allowances The Personal Allowance is frozen at £12,570 through at least the 2027/28 tax year, so these thresholds won’t move soon.7GOV.UK. Income Tax Personal Allowance and the Basic Rate Limit From 6 April 2026 to 5 April 2028 If you live in Scotland, the equivalent code is S0T, which applies Scottish income tax rates.2GOV.UK. Tax Codes – What the Letters Mean
What Happens After the Code Is Changed
Once HMRC approves a new code, they send your employer a notification called a P6. Payroll then applies the updated code and recalculates your tax for the rest of the year.8GOV.UK. Understanding Your Employees’ Tax Codes – Changes Any tax you overpaid on 0T is usually refunded automatically through your next payslip as a larger-than-normal net pay figure. You don’t need to file a separate claim.
If the update lands after your employer has already finalised a monthly payroll run, the corrected code and refund appear in the following month’s pay instead. Check your payslip to confirm the new code is showing. If it still reads 0T after two payroll cycles, contact HMRC again, because the P6 may not have reached your employer.
Reclaiming Overpaid Tax From Previous Years
If you were on 0T for part or all of a previous tax year, HMRC may owe you a refund for that year too. After each tax year ends on 5 April, HMRC runs an automatic reconciliation and sends a P800 tax calculation letter if you’ve overpaid.9GOV.UK. Tax Overpayments and Underpayments – If You’re Due a Refund
The P800 explains how much you’re owed and how to claim it. If it says you can claim online, you can request a bank transfer (which arrives within five working days) or a cheque (which takes up to six weeks). If the letter says HMRC will send a cheque automatically, expect it within 14 days of the letter’s date. If you’re owed money for more than one year, HMRC combines it into a single payment.
You have four years from the end of the tax year in which the overpayment happened to claim a refund. After that window closes, the money is gone. If HMRC is slow to process your repayment, they pay interest at 2.75% on the amount owed as of January 2026, calculated at one percentage point below the Bank of England base rate.