GST on FBT Calculator NZ 2026
This calculator works out the GST adjustment payable on fringe benefits, the extra line item on your IR420 quarterly (or IR421/IR422 annual) FBT return that sits alongside the FBT itself. Because FBT taxable values are GST-inclusive, the GST portion is extracted using the 3/23 formula rather than the usual 15 percent add-on. You start by confirming your GST registration status for the return period (fully registered, partially registered, or not registered), then enter the total taxable value from Box 3 of your IR420. From that figure you subtract any GST-exempt benefits, such as low-interest loans, superannuation contributions and life insurance, and any zero-rated benefits, leaving the GST-applicable taxable value the 3/23 formula is applied to. If you were only registered for part of the period, you enter the apportioned amount instead. There is also an optional field for employee contributions toward fringe benefits, since these create a separate GST supply reported in your regular GST return rather than the FBT return. The results show the taxable value breakdown, the GST-applicable amount, the GST adjustment to enter in IR420 Box 7 (or Box 6 annual), and, where relevant, the GST output on employee contributions for Box 5, plus a full step-by-step breakdown. It is an indicative guide only; confirm unusual or mixed benefits with a tax adviser or IRD before filing.
GST registration
Taxable benefits provided this period
Enter the total FBT taxable value from Box 3 of your IR420, then split between benefits that had GST in their cost versus those that did not.
Employee contributions (optional)
Why GST applies to fringe benefits
When a GST-registered employer purchases goods or services and claims back the GST as input tax, then provides those goods or services to an employee as a fringe benefit, the GST input credit needs to be effectively reversed. That reversal happens through the GST adjustment on the IR420 FBT return. The mechanic uses the 3/23 formula because FBT taxable values are GST-inclusive: a $1,150 GST-inclusive benefit contains $150 of GST (which is 3/23 of $1,150).
The GST adjustment is paid alongside the FBT itself, but it is a separate calculation. Box 7 of the IR420 (or Box 6 on the IR421/IR422 annual return) holds the GST amount, and Box 8 (or Box 7 annual) is the combined FBT plus GST due to IRD.
The 3/23 formula explained
NZ GST is 15%. If you have a GST-exclusive amount of $100, you add 15% to get a GST-inclusive amount of $115. The GST component is $15, which is $15/$115 = 3/23 of the GST-inclusive total. So when you have a GST-inclusive amount and want to extract the GST portion, you multiply by 3/23 (or equivalently divide by 7.667).
Example: A company provides an employee with a $2,300 GST-inclusive Christmas hamper. The FBT taxable value is $2,300. The GST adjustment is $2,300 × 3 ÷ 23 = $300. If FBT is at the 63.93% single rate, the FBT itself is $1,470.39. Total tax to IRD is $1,770.39 ($1,470.39 FBT + $300 GST).
Which benefits are GST-exempt for FBT purposes?
The following fringe benefits are excluded from the 3/23 GST calculation because the underlying supply is exempt from GST or zero-rated:
- Low-interest employment loans: Financial services are GST-exempt under section 14 of the GST Act.
- Superannuation contributions: Employer contributions to superannuation funds are an exempt financial service.
- Life insurance premiums: Life insurance is generally GST-exempt.
- Medical insurance premiums: Insurance services are typically GST-exempt for FBT purposes (check the policy specifics).
- Residential accommodation: Long-term residential accommodation provided as a benefit is GST-exempt.
- Bank fees and overseas bank charges: Financial services exemption.
Common GST-applicable fringe benefits (which DO attract the 3/23 adjustment):
- Motor vehicles for private use
- Goods and services provided to employees
- Vouchers and gift cards (with GST in their original purchase)
- Subsidised transport from a transport operator
- Entertainment that is not 50%-deductible food and drink
- Mobile phone use beyond the business tools exemption
Employee contributions create a separate GST supply
If an employee pays the employer toward a fringe benefit (such as contributing $50 toward fuel for a company car), the contribution is a separate supply for GST purposes. The employer must include the contribution in their regular GST return (box 5 income / output tax), with GST of 3/23 of the contribution amount. This is handled in the GST 101 / GST 103 return, NOT on the IR420.
The contribution also reduces the FBT taxable value: a $1,000 monthly vehicle taxable value reduced by a $200 employee contribution becomes $800 of taxable value for FBT, but the $200 contribution itself attracts $26.09 of GST in the regular GST return.
Partial GST registration
If you became GST-registered or de-registered partway through the FBT return period, GST applies only to the fringe benefits provided during the time you were registered. Apportion based on the dates benefits were provided, not the entire quarter. Use the "change GST amount" toggle in myIR to enter your manually-calculated amount, or note the apportionment on your paper return.
Sources
- IRD - GST for fringe benefit tax returns
- IRD - Work out taxable value and file FBT return
- IR409 Fringe Benefit Tax Guide - Part 8 GST on FBT (PDF)
- Goods and Services Tax Act 1985 Section 14 - Exempt supplies
This calculator provides an estimate only. Always verify your treatment with a tax adviser or refer to ird.govt.nz. The classification of a fringe benefit as GST-taxable, exempt, or zero-rated depends on the underlying supply, which can be technical for mixed benefits.
Related calculators
- FBT Quarterly Return Estimator - build the IR420 totals (use Box 3 output here)
- NZ FBT Calculator - calculate FBT on individual benefits
- GST Calculator - standard 15% GST add or extract
- Reverse GST Calculator - extract GST from a GST-inclusive amount
- FBT Attribution Calculator - Q4 wash-up calculation