Provisional Tax Safe Harbour — The Safety Net Most Tradies Don't Know About
Safe harbour is an IRD provision that protects you from use-of-money interest (UOMI) even if you end up underpaying provisional tax during the year.
The $5,000 Safe Harbour
If your prior year RIT was under $5,000, you're completely off the hook — no provisional tax required at all. Your full tax bill is simply due on 7 February after the tax year ends.
The Standard Uplift Safe Harbour
If your prior year RIT was $5,000 or more, you qualify for safe harbour if you pay at least the standard uplift amount (105% of prior year RIT) across three equal instalments on time. Even if your actual RIT turns out to be higher, IRD won't charge UOMI — provided you paid the standard uplift on schedule.
This is why the standard method is the safe choice for most tradies whose income is similar year to year.
When UOMI Applies
UOMI (currently 10.91% p.a.) applies when: - You use the estimation method and underestimate your RIT - You miss or underpay instalments under the standard method - Your final RIT is over $5,000 and you didn't pay the standard uplift
The UOMI charge runs from the instalment due date to the date you actually pay. On a $10,000 shortfall, that's roughly $1,091 per year — enough to hurt.
Mid-Year Income Drop
If your income has dropped significantly during the year (a slow patch, injury, or loss of a major client), you can switch to the estimation method and reduce your upcoming instalment. Just be conservative — underestimating carries UOMI risk. Talk to your accountant before making this call.