How to Check My Tax Code After a Job Change

Your first payslip at a new job is exciting. Your tax code on that payslip? Probably wrong.

Job changes are the single most common trigger for tax code errors in the UK, yet HMRC's own systems are not designed to catch them quickly. The result is that millions of employees quietly overpay or underpay income tax for months, sometimes years, after switching employer. If you've changed jobs in the last 12 months, this post is about the specific, structural reason your tax code deserves fresh scrutiny today.

Emergency Tax Code

A temporary tax code HMRC assigns when it lacks sufficient information about your income. The most common forms are 1257L W1/M1 (week 1/month 1 basis, meaning each pay period is taxed independently without reference to the year so far) and 0T (no personal allowance applied at all). Both typically result in overpayment.

Why Job Changes Break Your Tax Code

When you leave one employer, your old employer should issue a P45. This document tells your new employer three things: your tax code, how much you have earned so far in the tax year, and how much tax has already been deducted. Your new employer plugs those figures into payroll software, and in theory, you continue to be taxed correctly.

In practice, the P45 process fails regularly, and in the following predictable ways.

The P45 arrives late. Your old employer might issue it on your final day of employment, which can be days or weeks after your first payday at the new job. Your new employer has already run payroll without it. They default to an emergency tax code, and you overpay.

The P45 never arrives. Employers are legally required to provide a P45 but the penalty for failing to do so is not large enough to guarantee compliance. If you left on bad terms, or your old employer's HR administration was chaotic, you may simply never receive one.

You started a second job without a P45. If you're employed in two places simultaneously, the second employer almost always uses code BR or 0T, meaning every pound you earn there is taxed at 20 percent or higher with no personal allowance applied. That is correct if your first job already uses your full allowance, but it can be wrong if your income is split in a way that does not fully use the allowance at the primary job.

You moved from self-employment into employment. HMRC may not have updated its records quickly enough to assign a standard code. You may receive an OT or BR code by default.

The Code on Your Payslip Is Not a Guarantee

This is the part that most employees find genuinely surprising. Your tax code appearing on a payslip does not mean it has been verified. Your employer applies whatever code HMRC has issued or, in the absence of one, whatever default the payroll software assigns. Neither your employer nor the payroll software audits whether the code reflects your actual circumstances.

HMRC's Real Time Information (RTI) system, introduced in 2013, was supposed to make this more fluid. Employers now report payroll data to HMRC every pay period rather than annually, which gives HMRC a faster picture of what you've earned. But RTI does not automatically trigger a tax code correction when you change jobs. HMRC waits for information from both the old and new employer to reconcile, and that reconciliation can take months.

In the meantime, you are taxed on whatever estimate HMRC has made. If that estimate is wrong, you either overpay and wait for a refund, or underpay and receive an unexpected bill later. Neither is a comfortable position.

The only person with both the motivation and the information to catch this quickly is you. Checking your tax code at /check-my-tax-code takes minutes and costs nothing. Waiting for HMRC to fix it unprompted can cost you months of unnecessary deductions.

Reading the Signals on Your First Payslip

You don't need to be a tax expert to spot a problem. Look at your first payslip at the new job and check two things.

What code is shown?

The standard code for most UK employees in 2025/26 is 1257L. This reflects the personal allowance of £12,570. If your code is anything other than 1257L (or a variant that reflects a specific, known adjustment), treat that as a signal to investigate.

Codes that should prompt immediate action:

• 1257L W1 or 1257L M1: You're being taxed on a week 1 or month 1 basis. This is the emergency basis. HMRC does not have your year-to-date figures from your previous employment. You may be overpaying if you had income earlier in the tax year.
• 0T: No personal allowance is being applied. This is appropriate only in very specific circumstances (for example, you've already used your allowance elsewhere). In most cases, this means HMRC has no information about you at all.
• BR: All income taxed at 20 percent, no allowance. Often applied to second jobs, but sometimes applied incorrectly to primary employment.
• D0 or D1: All income taxed at 40 or 45 percent. Applied when HMRC believes all your allowance is used elsewhere. Worth verifying if you've recently changed jobs.

Is the tax deducted proportionate?

For a rough check: if you earn £50,000 per year, your monthly tax should be roughly £650 to £700 on a standard code. If you're seeing significantly more than this in month one, particularly if the payslip shows no year-to-date income carried forward, an emergency code is likely in play.

What to Do When the Code Is Wrong

Do not wait for HMRC to fix it. The passive approach costs you money for every week the wrong code remains in force. Here is the active approach.

Step 1: Check your Personal Tax Account

Log into your HMRC Personal Tax Account. Under the income section, you'll see the tax codes HMRC has issued for each employer on record. Check whether the code shown matches the one on your payslip. Also check whether your previous employer's income has been recorded. If HMRC doesn't have your P45 figures, the year-to-date income box may be blank or show zero, which explains why an emergency code was issued.

Step 2: Use a dedicated tax code checker

HMRC's Personal Tax Account tells you what code has been issued; it does not always tell you clearly whether it is correct for your circumstances. Check your tax code at /check-my-tax-code to get a clearer picture of what your code should be, based on your actual income situation, and whether the current one is likely costing you money.

Step 3: Contact HMRC directly

If a correction is needed, you can update HMRC by phone (0300 200 3300, PAYE helpline) or through the Personal Tax Account's income reporting section. Provide your P45 figures if you have them, or your approximate year-to-date income from your previous job. HMRC will then issue a revised code to your new employer, usually within a few weeks.

Step 4: Claim any overpayment

If you've been on an emergency code for several months and have overpaid, you can claim a refund. This does not happen automatically in most cases. If you're still employed, HMRC will usually adjust your tax code to give you the overpayment back through reduced deductions over the remainder of the tax year. If the tax year has ended, you'll need to either file a Self Assessment return or contact HMRC to request a P800 reconciliation.

For those who also have side income from self-employment, the How Do I Check My Tax Code? The Wrong Way Costs You post covers the additional complications that arise when PAYE and self-employment income overlap.

People also ask

What tax code should I have after starting a new job?

In most cases, 1257L on a cumulative basis, reflecting the standard personal allowance of £12,570 for 2025/26. If your employer does not have your P45, you may be placed on 1257L W1/M1 or 0T initially. Both are temporary emergency codes that should be corrected once HMRC receives your year-to-date income figures.

How long does it take for HMRC to correct an emergency tax code?

Typically four to six weeks if HMRC receives the necessary information automatically. However, if your P45 was not issued or your previous employer is slow to report data, the correction may not happen at all without you contacting HMRC directly. The fastest route is to log into your Personal Tax Account and report your income yourself.

Can I get a refund if my tax code was wrong after changing jobs?

Yes. If you overpaid due to an emergency tax code, HMRC will refund the difference. Within the same tax year, the refund usually comes via an adjusted code giving you lower deductions. After the year ends, contact HMRC or file a Self Assessment return to trigger a P800 calculation and cash refund.

Does starting a second job automatically put me on an emergency tax code?

Your second employer will typically use code BR (20% on all earnings, no personal allowance) unless you instruct otherwise. This is correct if your first job uses your full personal allowance, but could result in overpayment if your first-job income is below £12,570. Use the starter checklist your new employer provides to declare your situation accurately.

The Multiple-Jobs Complication

If you've changed jobs mid-year and also worked two jobs simultaneously at any point, your tax situation becomes meaningfully more complicated. Each employer operates independently; neither knows what the other is paying you. HMRC is supposed to coordinate, but the RTI data takes time to process and allocate correctly.

The practical result is that your combined tax across both employers may not equal what a single employer would have deducted on the total income. You might have two codes that together allow more allowance than you're entitled to (resulting in an underpayment bill later) or that together apply too little allowance (resulting in an overpayment). For a full breakdown of how multiple income sources interact, the HMRC Tax Code Checker: When to Trust It and When Not To post is worth reading alongside this one.

If you receive child benefit and your income has changed with the job move, check whether you now fall into the High Income Child Benefit Charge range (earnings over £60,000 in 2025/26). Your tax code may need adjusting to collect that charge, or you may need to register for Self Assessment. The salary tax calculator can help you model the net effect before you contact HMRC.

The Wider Pattern: Why HMRC Does Not Solve This Automatically

It is worth naming something plainly. HMRC collects the overpayment. While the money is technically yours and refundable, HMRC is not structurally incentivised to make the refund process fast or visible. The Personal Tax Account exists, and it is useful, but HMRC does not send a push notification saying "we think you've overpaid £400 this quarter." The burden is on you to check.

This is not a conspiracy. It is a capacity problem combined with a design problem. RTI improved things significantly, but the reconciliation of job-change data remains slow and partially manual. Until that changes, the most effective tax code audit is the one you run yourself.

As covered in Check Tax Code Online: What HMRC Shows vs Reality, what you see in the Personal Tax Account and what your employer's payroll system holds can diverge for several weeks after a change is requested. Always confirm the corrected code has appeared on your next payslip.

A Concrete Example

Dave is a maintenance technician earning £54,000 per year. He changes employer in October, halfway through the 2025/26 tax year. His P45 is delayed because his old employer used an external payroll bureau that didn't process leavers until the end of the month.

Dave's new employer puts him on 0T (no personal allowance) for November and December. At £54,000, the monthly difference between code 0T and 1257L is roughly £209. Dave loses £418 over two months to an incorrect code.

When HMRC eventually processes his P45 in January, they issue a corrected cumulative code that attempts to recover the overpayment through reduced deductions. But by then Dave has missed the calculation and assumes his lower January tax deduction is just normal fluctuation. The adjustment is spread across the remaining months of the tax year, invisible in the noise of monthly payslip variation.

Had Dave checked his tax code in November using /check-my-tax-code and contacted HMRC immediately, the correction would have come in December. He'd have recovered one month's overpayment faster and avoided January's complexity entirely.

The One Thing to Do Before Your Next Payday

You opened this post asking how to check your tax code. Here is the direct answer for anyone who has changed jobs: check it now, before your next payday, because that is the point at which another incorrect deduction becomes locked in for a month.

Look at your most recent payslip. If the code is anything other than 1257L on a cumulative basis, or if you've changed employer since April 2025, run a check at /check-my-tax-code today. Two minutes now could mean several hundred pounds back in your pocket before the tax year closes.

Job changes are exciting. Paying too much tax because of the paperwork that surrounds them is not. HMRC won't tell you the money is sitting there. That's why you have to check.

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