Need the short version?
Go back to the checker
If you already know the income type and just want the likely tax code, go straight back to the checker and answer the IR330 questions.
What tax code should I use?
Start with the broad question, then narrow it down by income type and IR330 path.
M vs ME tax code
Check when the main-income path stays on M and when ME or ME SL can apply.
Secondary tax codes
See the SB, S, SH, ST, and SA bands and when to add SL for student loan deductions.
IR330 vs IR330C
Work out whether you should use the employee declaration or the contractor withholding form.
IR330 form guide
See what the IR330 tax code declaration form is for and when IR330C is used instead.
RWT for dividends and interest
Check when investment income uses RWT instead of a normal employee tax code.
Need the follow-up answers?
Open the FAQ
If you need clarification on student loans, IR330 forms, or what changes during the year, the FAQ page is a faster read than the full guides.