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The short answer
New arrivals are often overtaxed because payroll does not yet have what it needs: in the UK, no P45 or starter checklist means an emergency tax code (ending W1, M1 or X); in Ireland, a missing PPS number or unregistered job means emergency tax. Once the tax authority sends payroll your correct details, the overpayment is normally refunded through your pay; in the US, students wrongly charged Social Security and Medicare ask the employer first, then claim from the IRS on Form 843.
Your first full pay abroad arrives and the tax line is far bigger than a colleague's on the same salary. That is common, not a sign you owe more. Tax systems that collect through payroll need to know your allowances, and until they do, payroll applies a cautious default.
Why it happens
- Payroll has no record of your previous income in the tax year, so it cannot give you the full allowance.
- Your tax or social security number is missing or not yet linked to the employer.
- You were put on the wrong category, for example taxed as a second job.
- As a student, you were charged social security you are exempt from.
United Kingdom: emergency tax codes
GOV.UK says 1257L is the code used for most people with one job, and that codes ending in W1, M1 or X are emergency codes, a sign HMRC has not yet matched your full details to the job. GOV.UK adds that HMRC may take up to 35 days from your start date to update your code, that a new code is sent to you and your employer within 15 working days, and that monthly-paid staff usually see it on the next or following payslip.
What to do
- Give your employer the right starter information. If you had a UK job earlier in the tax year, hand over parts 2 and 3 of your P45. GOV.UK says a lost P45 cannot be replaced, so use the starter checklist instead.
- If this is your first UK job, complete the starter checklist your employer gives you, answering each statement about other jobs and income since the tax year began.
- Check your code in your HMRC personal tax account or the HMRC app, and tell HMRC if it is wrong.
- Watch the following payslips. GOV.UK says once the code is corrected, overpaid tax is refunded through your pay.
If you leave before the refund catches up, it may come when the next employer uses your P45 or after the tax year ends. Keep every payslip and the P45 from each job.
Ireland: emergency tax until Revenue has your details
Revenue says you pay emergency tax where you have not given your employer your PPS number or the job is not registered. Its guidance on stopping emergency tax sets out the steps:
- Get a PPS number from the Department of Social Protection if you do not have one.
- Register for myAccount and use PAYE Services, "Add Job or Pension Details", entering your PPS number, the employer's tax registration number and your start date.
- Revenue issues a Revenue Payroll Notification (RPN) to the employer showing your tax credits and rate bands.
- Once a cumulative RPN is in place, Revenue says overpaid income tax and USC are refunded through payroll.
United States: withholding and student FICA
US income tax withholding is driven by your Form W-4. The 2026 form explains the steps for dependants, other income and deductions; filling it in accurately avoids most over-withholding, and any overpayment is otherwise settled when you file your tax return. The IRS says nonresident alien F-1, J-1 and M-1 students in the US for fewer than five calendar years are generally exempt from Social Security and Medicare taxes on authorised work. If those taxes were withheld anyway, the IRS says to ask the employer for a refund first; if you cannot get a full refund, file Form 843 with Form 8316 and supporting documents.
A worked example of what is at stake
Example figures for the UK: a new arrival starts in October on £2,500 a month. On 1257L, monthly tax would be (£2,500 − £1,047.50) × 20% = £290.50. If payroll instead gave no tax-free allowance at all for the month, basic-rate tax would be £2,500 × 20% = £500.00. The difference, £500.00 − £290.50 = £209.50, shows the scale of what can be overpaid each month until the code is fixed (example, basic rate only). The letters in a code matter; GOV.UK's tax codes page explains each of them, including 0T and BR.
Records to keep
- Every payslip, and the P45, P60 or year-end summary from each job.
- Letters or notices from the tax authority about your code or credits.
- Your tax and social security numbers, and the employer's reference.
- Dates you arrived and started work, which matter for residence tests; see tax resident in two countries.
For a line-by-line guide to the payslip itself, see reading the deductions on your first payslip.
Where Pryme fits
Every Personal Account customer can set up a Personal Assistant Agent that keeps track of reminders, so a follow-up such as checking whether next month's payslip shows the corrected code is not forgotten; nothing moves without your approval (Personal Assistant). Refunds arriving in pounds, euros or dollars can stay in that currency in a Pryme account until you choose to convert (multicurrency account).
Questions people ask
What does W1 or M1 mean on my tax code?
GOV.UK says codes ending in W1, M1 or X are emergency codes. They usually apply until HMRC sends your employer a corrected code.
How long does it take to get off emergency tax in the UK?
HMRC may take up to 35 days from your start date to update your code. Monthly-paid staff usually see the change on the next or following payslip, with overpaid tax refunded through pay.
How do I stop emergency tax in Ireland?
Give your employer your PPS number and register the job in Revenue myAccount under PAYE Services. Overpaid income tax and USC come back through payroll once a cumulative RPN is in place.
Can F-1 students get FICA refunded?
Yes, if exempt. The IRS says ask the employer first, then file Form 843 with Form 8316 if a full refund is not possible.
Sources
- GOV.UK: Tax codes · accessed Oct 2026
- GOV.UK: PAYE forms, P45 · accessed Oct 2026
- Revenue: How to stop paying emergency tax · accessed Oct 2026
- IRS: Foreign student liability for Social Security and Medicare taxes (reviewed 18 Aug 2026) · accessed Oct 2026
- IRS: Form W-4 (2026) · accessed Oct 2026
- GOV.UK: Income Tax rates and Personal Allowances · accessed Oct 2026
This article is general information, not financial, legal or tax advice. Products described are provided under the terms on this site and are subject to regulation and eligibility.