My payslip has BR, D0, K, M1 or a strange code
Decode the code first, then check whether it is temporary, split across jobs, or recovering an underpayment.
Pick the HMRC problem
I received a P800, P2, SA250, SA316 or penalty notice
Identify the document type before you pay, appeal, ignore or call HMRC.
I think I was put on emergency tax
Estimate the likely refund route and whether the issue is payroll timing or a code correction.
I am not sure whether I need Self Assessment
Use the readiness checklist before waiting for a letter or missing a deadline.
I need to know what is due and when
Use the calendar for January filing, payments on account, year-end and April reset dates.
My income changed and the tax feels wrong
Run the income baseline after decoding the letter or code so the numbers make sense.
Do not skip the evidence step
| Before you respond | Why it matters |
|---|---|
| Take a photo or download the document | You need the reference, date, tax year and exact wording if you challenge or compare later. |
| Check the tax year | Many HMRC letters relate to a previous tax year, not the payslip you are looking at now. |
| Compare with payslips, P60 or P45 | The quickest fix is often spotting which employer, pension provider or benefit is driving the code. |
| Save a scenario | Keep the calculation that explains why you think the result is right or wrong. |