Tax Codes for Kiwis with a Side Hustle: Don't Get Hit With a Bill

One of the most expensive admin mistakes Kiwis make: getting your tax code wrong on a side hustle. The damage usually shows up as a surprise bill from IRD in May, a year after the income was earned and spent.

This is the plain-English fix.

Why your tax code matters

NZ income tax is progressive — the more you earn, the higher the rate on each additional dollar. PAYE (Pay As You Earn) is calculated by your employer based on the tax code you give them.

The system assumes each employer is your only employer. So if you give two employers an "M" code (your main job), they BOTH calculate PAYE assuming you only earn what they pay you. Both apply low-rate tax to the early thousands. Result: total tax paid is way under what you actually owe.

IRD catches this at the end of the year. You get a bill. Sometimes a big one.

The codes you need to know

For most Kiwis with a side hustle, only four codes matter:

• M — Main job, no student loan
• M SL — Main job, has student loan
• S — Secondary job, total income from all sources is under $48,000
• SH — Secondary job, total income from all sources is $48,001-$70,000

There are others (ST, SB, CAE, etc.) but unless you're in unusual circumstances those four cover 95% of cases.

The key concept: your MAIN job uses M (or M SL). Every other employer — Uber, freelance gigs paid via PAYE, weekend retail shifts, anything with a regular paycheck — uses S, SH, or ST.

Walk through: a real-world example

You earn $55,000 from a 9-5 office job (your main job).

You also earn $10,000/year from a Saturday hospitality shift.

Your TOTAL income is $65,000, which falls in the $48,001-$70,000 band. So:

• Main job: M (or M SL if student loan)
• Saturday job: SH — because adding the side income pushes your total into the 30% band

If you accidentally tell the Saturday employer "M" too:

• Main job withholds correctly for $55,000
• Saturday job withholds as if YOU only earned $10,000
• Both apply the 17.5% rate to your Saturday income (correct for $10k alone)
• But $4,000 of your Saturday income should have been taxed at 30%
• IRD bills you for the difference: roughly $500

If you accidentally use S instead of SH (also wrong since SH is the right band), you'd pay 17.5% instead of 30% on your Saturday income — a smaller but still real underpayment.

How to figure out your right code

The official IRD tool is at ird.govt.nz/tax-rates-codes/work-out-tax-code. It asks five questions and spits out the right code in 60 seconds.

But the heuristic that catches 95% of people:

1. Add up your expected gross income for the tax year from ALL sources (main job + every side gig).
2. If total < $14,000 → main job M, any others S
3. If total $14,001-$48,000 → main job M (or ME), any others S
4. If total $48,001-$70,000 → main job M, any others SH
5. If total > $70,000 → main job M, any others ST

If you have a student loan, append "SL" to your main job code (e.g. M SL, ME SL).

Common side-hustle scenarios

Scenario 1: Uber / DoorDash / Uber Eats

These platforms are NOT PAYE employers — you're a contractor. They don't withhold tax. You're responsible for it yourself.

You'll receive 1099-equivalent forms (or just the platform's earnings summary) at year-end. You declare it on your tax return as schedular or self-employed income.

You don't pick a tax code for this kind of work — you just need to either pay provisional tax (if income is significant) or save 30%+ of every payout for the eventual bill.

Scenario 2: Freelance / contracting work paid via invoice

Same as Uber — you're a contractor, not an employee. No tax code applies. You're responsible for setting aside tax yourself.

Scenario 3: A second PAYE job (retail, hospitality, weekend casual)

This IS where tax codes matter. Use S or SH based on your total income. NOT M.

Scenario 4: Your "main job" income changes mid-year

If you get a raise that pushes your total over a band threshold, change your secondary code with your other employer ASAP. Don't wait until end of year. You can do this through myIR.

The student loan trap

If you have a student loan and a side hustle, both employers should know about the loan. Otherwise repayments don't get deducted properly.

For your main job: use M SL (not just M).

For your side job: still use S or SH as appropriate — student loan repayments are added on top automatically based on combined income, not via the secondary code.

If your total income is under the repayment threshold (~$24,000 in 2026), no student loan deduction happens. Above that, the standard 12% applies on every dollar over the threshold.

What to do if you've already screwed it up

Don't panic. Most tax-code mistakes are catchable and fixable.

1. Log into myIR and check what each employer is using for your code
2. If wrong, change it via myIR (takes 2 minutes per employer)
3. The change applies to future pays only — past underpayment will still need to be paid
4. IRD will auto-assess at year-end and either bill you or refund you
5. If you owe more than $500, IRD will set up a payment plan — call them, don't ignore the letter

If you're owed money (you over-withheld), it'll come back as part of the auto-assessment refund.

How to never have this happen again

The single best habit: whenever you start a new income stream, immediately update myIR. Five minutes that prevents a $500-$2,000 surprise twelve months later.

If you're a contractor or freelancer (Scenario 1 or 2 above), set up an [automatic payment](/glossary/automatic-payment) that moves 30% of every payout to a separate "tax" savings account. Then when the IRD bill arrives, it's already paid for.

That's the difference between people who get hit with bills and people who don't — not knowledge of tax codes, but a system that handles it automatically.

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Steady automatically categorises every payment from your bank, including unusual ones like IRD refunds and side-hustle deposits. Setting up a separate "tax savings" goal for 30% of side income is one of the most popular use cases — turns the next IRD bill into a non-event.