1. Capture four facts from your first payslip
Write down your start date, pay date, full code and tax basis. Then record taxable pay and Income Tax for the period, plus the year-to-date figures. Look for an old-employment pay or tax line as well. Send that compact record to payroll if something needs explaining.
A lower first payment can also reflect a partial month, pension enrolment, a loan deduction or payroll cutoffs. Read those lines before assigning the entire difference to emergency tax. Conversely, a payslip with no emergency suffix can still contain an incorrect income record.
BR and 0T are not interchangeable with M1. BR taxes income from that job at the basic rate; 0T means no Personal Allowance is applied and may arise where details are missing or the allowance has been used. HMRC's emergency classification depends on the suffix/basis. What codes mean
For a general explanation of the familiar standard code, use the 1257L guide. This page focuses on the job-change handover and correction process.
2. Check the P45 handover
Your P45 records pay and tax since 6 April up to leaving, as well as the leaving date and tax code. Give it to your new employer; with a paper form, keep Part 1A and hand over Parts 2 and 3. If the old employer has not supplied one, ask for it. A lost P45 cannot be replaced, so use the starter checklist instead. GOV.UK: P45
Check the numbers against the final old-job payslip. If pay or tax is wrong, ask the previous employer for a correction. Be precise about whether a final bonus, holiday payment or other payment appears in that record. Repeating the wrong figures to the new employer will not repair the underlying mismatch.
Ask new payroll whether they received and processed the P45 before the relevant cutoff. A document sent after payroll closed may explain why the first payslip still uses temporary details. Keep the sent date and payroll's acknowledgement so you can check the following run.
3. If there is no P45, use the starter checklist accurately
The checklist gives the new employer information needed to establish a starter declaration. It asks about your situation, rather than inviting you to select whichever answer produces the lowest immediate tax. Tell payroll if another job is continuing or if your circumstances changed between completing the form and starting.
The employer's official guidance identifies the P45 and starter checklist as the main sources for setting up the employee record. HMRC: employee information
Do not send a spreadsheet that subtracts your old tax from your new salary as a substitute for the documents. Use that spreadsheet as your own checking aid. Payroll needs the official figures and declaration, while HMRC needs a consistent picture of the employments.
4. Understand the timing without promising a payday
HMRC's emergency-code guidance says the new-job tax-code update can take up to 35 days from starting, after the employers supply the necessary details. If you started more than 35 days ago and the code still looks wrong, follow its correction route. HMRC: new-job code update
There is a separate timing statement for viewing the new employment online: HMRC says those details will be available within six weeks after your first payday. That concerns the online employment record, not a six-week promise to issue a code or pay a refund. The two timings have different starting points and should not be substituted for each other. Tell HMRC about a new job
A code update and a refund are separate milestones. When HMRC has all the necessary income details, a corrected-code refund is normally delivered through pay. A monthly employer should generally apply the new code on the next or following pay; weekly payroll uses different timing. HMRC refund process
Record the code-notice date and the next payroll date. If the expected change does not appear, ask whether payroll received the notice in time. Avoid budgeting for a refund before its amount and processing are confirmed.
Worked checks: why the same code can produce different cash flow
The first check illustrates one month's allowance. The second compares Month 1 treatment with a cumulative calculation after six months without income.
Example 1: one month's allowance under M1
Worked example
Assume a £3,000 monthly payment in 2026/27, standard £12,570 allowance, no other deductions, and England/Wales/Northern Ireland. One twelfth of the allowance is £1,047.50. The simplified taxable amount is £1,952.50, giving £390.50 Income Tax at 20%. This is an illustration of the period calculation, not evidence that the person overpaid.
Example 2: the first pay follows six months without income
Worked example
Assume the same £3,000 is the person's first and only earnings up to tax month seven, with no taxable benefits or other income and the full standard allowance. Seven twelfths of £12,570 is £7,332.50. A cumulative calculation has enough allowance to cover the £3,000 so far, while M1 still uses only £1,047.50. The simplified difference at that point is £390.50.
This does not mean every new starter gets seven months' allowance or that the eventual year-end bill is zero. It depends on the actual income and tax history. Someone who earned £30,000 in the previous job has a very different cumulative record from someone who earned nothing.
A useful message to payroll
“Please check my full code and cumulative basis, whether my P45 was processed, and the previous pay and tax figures used. I started on [date]; my P45 was supplied on [date]; the payslip is dated [date]. Please explain any difference between the P45 and payroll record.”
That gives payroll a concrete discrepancy to investigate. If payroll confirms it is using HMRC's latest instruction, check HMRC's employment record and expected annual income next. Keep the old job's leaving date and any overlap clear.
Common questions
Is emergency tax a higher fixed tax rate?
No. It changes the calculation basis; it does not create a universal emergency percentage. Depending on the circumstances, temporary treatment can collect too much or too little.
Should I always be on 1257L?
No. Benefits, multiple employments and other adjustments can justify a different code. Scottish codes also carry an S prefix, and Welsh codes can carry C.
Can Afterax predict the refund?
The income-tax calculator helps estimate a full-year liability. It does not reconstruct P45 history or issue HMRC refunds. Compare the annual estimate with complete records, then use the official correction process.
Sources
Primary references checked 24 October 2026.