Emergency tax codes such as W1, M1, X or NONCUM can change how PAYE tax is taken when payroll is not using full cumulative year-to-date details.
The short answer
Emergency tax usually means PAYE is being worked out on the current week or month rather than full year-to-date pay. Codes ending W1, M1, X or NONCUM are non-cumulative and can make a first or changed payslip look different from an annual salary estimate.
Fictional payslip diagram highlighting the tax-code area. Real labels vary by employer and payroll provider.
Model an emergency tax-code marker
Enter a code from a payslip, HMRC account or payroll notice. Examples: 1257L W1, 1257L M1, 1257L X, BR M1 or 0T W1.
1257L W11257L M11257L X1257L NONCUMBR M10T W1
Normalised code1257L M1
Modelling statusUse caution
Region basisEngland/NI
Emergency markerM1
1257L M1 allowance-style code
For modelling in PayBreakdown, 1257L M1 usually means about GBP 12,570 of tax-free pay is applied before PAYE Income Tax is estimated.
The L suffix usually means the person is entitled to the standard tax-free Personal Allowance.
PayBreakdown uses the allowance in the code alongside salary, region, pension and student-loan assumptions.
Check your payslip, HMRC account or payroll if the code has changed or includes adjustments you do not recognise.
PayBreakdown can show the tax-code input, but it does not recreate exact weekly or monthly payroll timing.
Emergency markers can make a payslip differ from an annual calculator estimate.
PayBreakdown does not decide payroll correctness, lender approval, benefit entitlement or employer compliance, and does not give regulated financial, mortgage, debt, tax, payroll or legal advice.
What W1, M1, X and NONCUM mean
These markers usually mean the payroll calculation is non-cumulative for the pay period. PayBreakdown can model the tax code effect, but it is not a full emergency-tax calculator yet.
Emergency tax codes usually mean PAYE is using the current week or month rather than full year-to-date pay details.
W1 is used when someone is paid weekly and payroll is not using full cumulative year-to-date pay.
M1 is used when someone is paid monthly and payroll is not using full cumulative year-to-date pay.
X is used where pay dates vary.
NONCUM may appear in payroll software for the same non-cumulative emergency basis.
Emergency-code calculations can mean too much or too little tax is deducted in a pay period.
Emergency tax is common when starting a new job and payroll does not have previous income and tax details.
A P45 can help a new employer update the tax code.
HMRC may update the tax code after receiving details from current and previous employers.
Why it can happen
Emergency tax is common around job changes, missing previous pay details, new benefits or State Pension changes. HMRC may later update the code after receiving employer or pension-provider information.
Check the tax code shown in the HMRC online service or HMRC app against the code on the payslip.
Check employment, pension, estimated taxable income, company benefit and expense details in the HMRC service.
If the payslip code differs from the HMRC record, ask payroll whether the latest HMRC notice has been applied.
If a code changes, HMRC sends the new code to the individual and to the employer or pension provider.
PayBreakdown can compare estimates, but it cannot correct a code or confirm a payroll issue.
How to use PayBreakdown
Use the salary calculator to compare the emergency code against a standard-code estimate, then check the payslip code against HMRC and payroll records.
This limited helper explains emergency and non-cumulative markers for PayBreakdown modelling. It is not an emergency-tax calculator, refund estimator or tax-code correctness checker.
PayBreakdown can model the base tax-code effect where supported, but it does not run a true week-by-week or month-by-month non-cumulative payroll calculation.
Check your payslip, HMRC account or payroll if unsure. This does not prove an error or refund.
PayBreakdown tax-code output is an estimate only and is not tax, payroll, employment, legal, accounting or financial advice.
What this page cannot decide
This page explains emergency-code markers for modelling. It does not decide whether a code is correct, whether payroll has made an error, or whether a refund is due.
True non-cumulative payroll treatment can be period-specific, so PayBreakdown does not run a full week-by-week or month-by-month emergency-tax calculation.
Use this as an estimate and check HMRC or payroll if the payslip code is unexpected.
Do not treat a calculator difference as proof of a payroll, HMRC or employer issue.
What this answer does not decide
This is educational guidance on how UK pay and tax work. It does not decide payroll correctness, HMRC treatment, lender approval, benefit entitlement or employment rights, and it is not regulated financial advice. Where a figure matters, check it against your payslip, your HMRC account, or the official guidance linked above.
GOV.UK lists W1, M1, X and NONCUM as emergency tax markers. They mean PAYE is not using the full cumulative year-to-date basis for that pay period.
Why can emergency tax make a payslip look high-taxed?
On a non-cumulative basis, payroll may tax the current week or month as if that pay level continues for the year, so a single payslip can look different from an annual estimate.
Can PayBreakdown calculate exactly when emergency tax ends?
No. PayBreakdown can compare estimates, but HMRC and payroll records determine when a code changes from emergency to cumulative treatment.
What should I check if I see W1 or M1 on a payslip?
Check the code in HMRC's service or app, compare it with the payslip, and check whether payroll has P45 or starter details. The estimate is not tax or payroll advice.
Last updated 2026-08-27. Checked by Sean Elsmore. Rates last checked against GOV.UK on 2026-08-07. Estimates are for planning and should be checked against official records where the decision matters.