Check My Tax Code Is Correct: The New Job Problem

Your first payslip from a new employer should feel like a fresh start. Too often, it marks the beginning of a quiet overpayment that runs for months before anyone notices.

If you have recently changed jobs and you want to check your tax code is correct, the odds are not in your favour. HMRC's own data shows that tax code errors spike precisely at employment transitions, and the most common direction of error is the one that costs you money, not HMRC. This post is specifically for PAYE employees who have moved jobs, started a second role, or rejoined the workforce after a gap, and who suspect something is off on their payslip.

Why Job Changes Break Tax Codes

HMRC operates on the assumption that it always has an accurate, up-to-date picture of your income. In practice, the system relies on a chain of data handoffs: your previous employer submits a P45, your new employer enters those figures into their payroll software, and HMRC adjusts your code accordingly. Break any link in that chain and the system defaults to emergency settings.

Here is where it goes wrong in real life:

Your P45 arrives late or not at all. Some employers are slow to issue P45s. Others send them to old addresses. If your new employer starts payroll without that document, they are obliged to put you on an emergency tax code, most commonly 1257L W1/M1 or 0T.

You started mid-year after a gap. If you were unemployed, travelling, or on a career break before your new role, HMRC's system may treat your new income as if it is annualised from day one of the tax year. The result is a tax code that overtaxes you to account for income you never received.

You have two jobs simultaneously. If you left one job and started another on the same date, or if you have a side role alongside your primary employment, HMRC must decide which job gets your personal allowance. It frequently gets this wrong. See Is My Tax Code Correct? The Multiple Income Problem for the full breakdown on this scenario.

Your new employer made a data entry error. Payroll is handled by humans, and humans mistype figures. A salary entered as £35,000 when it should be £53,000 produces a different tax code, and HMRC will trust the employer's submission unless you challenge it.

Emergency Tax Code

A temporary tax code HMRC assigns when it does not have enough information about your income. The most common versions are 1257L W1/M1 (which taxes each pay period independently, ignoring the rest of the year) and 0T (which applies no personal allowance at all). Both frequently result in overpayment and should be corrected as soon as your circumstances are confirmed.

The Real Cost of Getting It Wrong

An emergency code is not a minor inconvenience. Take a standard employee earning £52,000 a year. Under the correct 1257L code, they should pay roughly £10,232 in income tax annually. Under code 0T, with no personal allowance applied, they pay closer to £13,632 a year, a difference of £3,400 in HMRC's favour. Even on a monthly basis, that is over £280 disappearing from every payslip.

For someone on a more typical £35,000 salary, the difference between the correct code and 0T is around £2,570 per year. That is not a rounding error. That is a holiday, a car service fund, or several months of a utility bill.

The cruellest part is timing. Emergency codes are most likely to appear on your first payslip, the moment when you are busiest settling into a new role and least likely to scrutinise a payroll document. HMRC counts on this inertia.

How to Check Your Tax Code Is Correct Right Now

Do not wait for your employer to flag this. Do not wait for HMRC to write to you. Here is what to do today.

Step 1: Find your current tax code

Your tax code appears on your payslip, usually labelled clearly. It will look something like 1257L, 1257L W1/M1, 0T, or BR. Write it down before you go any further. If you have recent payslips from both your old and new employer, check both. You are looking for a mismatch or an emergency code.

Step 2: Understand what your code should be

For most single-job PAYE employees, the correct code for 2025-26 is 1257L. This reflects the standard personal allowance of £12,570. If your code is anything other than 1257L, there should be a reason. Common legitimate reasons include:

• Underpaid tax from a previous year being collected through your current code (your code will be lower than 1257L)
• Taxable benefits in kind from your employer, such as a company car (also reduces your code)
• You earn over £100,000 (your allowance tapers and your code reflects that)
• You have opted for an adjusted code for another reason

If none of those apply and your code is not 1257L, you may be on a wrong code.

Step 3: Log in to your Personal Tax Account

Go to gov.uk and access your Personal Tax Account using Government Gateway. Under the PAYE section, you can see the tax code HMRC holds for each of your employments, including the breakdown of what has been added or removed from your allowance and why. This is the most reliable source because it shows what HMRC's system actually believes about you, not just what your employer was told.

If you would rather use a faster route, check your tax code at /check-my-tax-code to see where you stand without navigating government portals.

Step 4: Look for these specific red flags

• W1 or M1 suffix. This means "week 1" or "month 1" basis. Your employer is taxing each pay period in isolation, without reference to what you have already earned and paid this year. This often results in overpayment if you started the job partway through the tax year.
• 0T code. No personal allowance whatsoever. Almost certainly wrong unless you earn over £125,140.
• BR code. All income taxed at basic rate (20%). This is typically used for a second job where the personal allowance is already used elsewhere, but it is frequently applied in error to primary jobs.
• Multiple codes for one employer. Sometimes a system glitch results in duplicate entries. Check that HMRC's records show only one live code per employment.

Step 5: Contact HMRC to correct it

If you spot an error, do not wait for the annual reconciliation. Call HMRC's income tax line on 0300 200 3300 or use the online query form in your Personal Tax Account. Have your National Insurance number, your employer's PAYE reference (found on your payslip), your current tax code, and what you believe the correct code should be.

HMRC typically corrects codes within a few weeks. Any overpaid tax from the corrected period will then be automatically refunded through your payslip, or via a cheque or bank transfer if the tax year has already ended.

What Happens to Tax You Already Overpaid

This is the question most people forget to ask. You spotted the error in June. What about March, April, and May?

If the tax year is still open, once HMRC corrects your code, your employer adjusts your tax deductions for the remaining months to account for the overpayment. In effect, you pay less tax in the later months to balance what you overpaid earlier. No action needed beyond the initial correction.

If the tax year is closed, that is 5 April has passed, HMRC should automatically reconcile your account using the P800 process. This compares what you actually paid against what you should have paid and issues a refund if you overpaid. The P800 typically arrives by post between June and October after the tax year ends.

However, the P800 is not infallible. HMRC's reconciliation depends on data from your employers, and if any of that data is wrong, the P800 will be wrong too. If you believe you have overpaid and have not received a P800 by November, contact HMRC directly to initiate a check. You can claim back overpaid tax going back four tax years.

For a broader look at how HMRC's year-end reconciliation can miss errors, Tax Code Correct? What HMRC Gets Wrong at Year End is worth reading alongside this.

The Emergency Code Myth Worth Busting

One of the most persistent misconceptions is that an emergency tax code is temporary and self-correcting. The logic goes: HMRC will sort it out eventually, it will all come back in the reconciliation, nothing to worry about.

This is partly true and mostly dangerous. Yes, overpaid tax can be recovered. No, it is not always automatic. The reconciliation system missed an estimated 5.5 million cases requiring a correction in a single recent tax year, according to HMRC's own published figures. Some of those were underpayments that led to unexpected bills. Many were overpayments that sat quietly in HMRC's coffers because nobody chased them.

You are not owed interest on overpaid tax in most cases. You are not notified proactively if HMRC holds an overpayment. The burden of claiming is yours. Thinking of it as a temporary inconvenience that will fix itself is exactly the mindset that leaves money with HMRC rather than with you.

If You Changed Jobs and Have a Company Benefit

One more scenario worth flagging: if your new job includes taxable benefits in kind such as private medical insurance, a company car, or a season ticket loan, these reduce your tax-free allowance and should change your code.

If your new employer submitted a P11D or payrolled benefits information to HMRC but your previous employer did not, or vice versa, your code may reflect a benefit you no longer have, or fail to reflect one you do. This is a surprisingly common source of error at job transitions and it can go in either direction: overpaying or underpaying. For more on how life changes affect your code, Check My Tax Code Online After a Life Event covers this territory in detail.

If you have a child benefit claim and your salary has changed materially because of the job move, it is also worth checking your position on the High Income Child Benefit Charge. The threshold is £60,000, and moving into or out of that bracket has tax consequences that may not automatically update your code. The child benefit tax calculator can help you model the impact.

People also ask

What tax code should I be on when I start a new job?

For most employees with one job and no unusual circumstances, the correct code for 2025-26 is 1257L. If your new employer does not receive your P45 in time for the first payroll run, they may put you on an emergency code such as 1257L W1/M1 or 0T temporarily. You should check your code on your first payslip and correct it promptly if it looks wrong.

How long does it take HMRC to fix a wrong tax code?

Once you notify HMRC of an error, corrections typically take two to four weeks. Your employer will then apply the new code from the next payroll run. Any overpaid tax within the same tax year is usually recovered automatically through reduced deductions in subsequent months.

Will I automatically get a refund if I was on the wrong tax code?

Not always automatically. If the tax year is still open, the correction flows through your remaining payslips. If the tax year has ended, HMRC should send a P800 reconciliation notice, but this process can miss errors. If you believe you have overpaid and have not heard from HMRC by November after the tax year ends, contact them directly to claim your refund.

What does the W1 or M1 suffix mean on my tax code?

W1 means week 1 basis and M1 means month 1 basis. Both indicate that your employer is taxing each pay period in isolation rather than on a cumulative basis. This is common after a job change and often results in overpayment if you joined partway through the tax year. It should be corrected as soon as HMRC has your full income picture.

A Quick Reminder: Where to Check

If this article has prompted you to look at your payslip with fresh suspicion, that is exactly the right instinct. Your first port of call is your Personal Tax Account at gov.uk. Your second is /check-my-tax-code, which can help you understand what your code means and whether it looks right for your situation.

If your circumstances are more complex, perhaps you have a salary above £100,000 or multiple income sources, the multiple income tax calculator can give you a clearer picture of where your overall liability should sit.

You started a new job. You should not also be starting an accidental loan to HMRC.

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