Most emergency tax is refunded through your pay rather than claimed. Once HMRC sends your employer a cumulative code, the payroll works out your tax for the whole year to date, compares it with what you have already paid, and gives the difference back in your next payslip. That route depends on HMRC holding your income details for the year; where it does not, the correction waits until after 5 April and HMRC writes to you.
First, check that you have overpaid
An emergency code does not always take too much. It gives you one pay period's worth of allowance and no memory of the rest of the year, so it overcharges someone who started late in the tax year and can undercharge someone who moved from a better-paid job to a worse-paid one.
The test is the year, not the month. On £30,000 a year with code 1257L, a full tax year produces £3,486.00 of income tax, which is £290.50 a month and leaves £2,093.34 of take-home pay. Compare that with the income tax on your payslips so far, and the gap is roughly what is outstanding in either direction.
It is an approximation until the year has run its course, because a cumulative code settles the year rather than any one month. What it tells you reliably is whether the difference is pennies or hundreds of pounds.
The route that needs nothing from you
The refund normally arrives without a claim. When HMRC replaces the emergency code with a cumulative one, your employer applies it on the next pay run. The payroll adds up your pay and tax since 6 April, works out the tax due on the year so far, and deducts the difference, which can be a negative number.
Paid monthly, that is typically your next payslip or the one after. Paid weekly, typically the third. The refund shows up as a lower tax figure or as a minus in the tax column rather than as a separate payment.
A monthly payslip on an emergency code gives you £1,048.26 of tax-free pay and no more. The moment a cumulative code arrives, every unused month of allowance since 6 April comes back into the sum at once, which is why the correcting payslip can look surprisingly large.
What actually speeds it up
Give your new employer your P45 if you have one. It carries your pay and tax to date from the old job, which is exactly what a cumulative calculation needs. If you do not have a P45, fill in the starter checklist and answer the statements accurately, because the answer decides the code your employer uses on day one.
Then check what HMRC holds about you in the check your Income Tax service: your employments, your pensions, your estimated income for the year, and any company benefits. A code is rebuilt from that record, so correcting it there is what produces a new code.
After starting a new job, GOV.UK asks you to allow 35 days for your income details to reach HMRC before getting in touch. Contacting HMRC earlier than that rarely changes anything, because the information the new code depends on has not arrived yet.
If the tax year has already ended
Payroll cannot refund tax for a year that has closed. After 5 April, HMRC reconciles the year against what every employer and pension provider reported, and if you have paid too much it writes to you with a tax calculation, the letter known as a P800.
The letter says how the refund will be paid. Some are paid online from your personal tax account, and where that route is not used, HMRC sends a cheque. Either way the calculation itself arrives without a claim, and the thing worth doing is checking it against your P60 and your payslips rather than assuming it is right.
If you left a job part-way through a year and had no other income afterwards, the refund can be claimed rather than waited for. That is a specific claim about a specific circumstance, and the GOV.UK page on claiming a refund when you have stopped working sets out which form applies.
How far back a refund can go
Overpaid tax can be reclaimed for earlier tax years as well as the current one. HMRC sets a time limit for each year, and a year that is already closed is claimed rather than corrected through payroll.
Your P60 for each year is the document the claim rests on: it certifies what you were paid and what was deducted, which is why keeping them matters more than keeping payslips.
A note on refund companies
Claiming through HMRC is free, and the payroll route costs nothing and needs no claim at all. Companies that offer to reclaim tax for you charge a share of the refund and often ask you to sign an assignment that sends future repayments to them as well.
We do not recommend for or against using one. What is worth knowing before you sign anything is that the same claim can be made directly, and that an assignment can cover more than the one refund you had in mind.
Nothing has arrived. What now?
Check the code on your latest payslip first. If it still ends in W1, M1 or X, the new code has not reached your employer and that is the thing to chase; employers can confirm which code they are using and when it arrived, though they cannot change it themselves.
If the code has changed and the refund has not appeared within two pay runs, the year-to-date columns will show whether the payroll has taken the earlier months into account. Where they have not, the usual cause is a code issued on a week 1 or month 1 basis, which looks like a new code but behaves like the old one.