Reverse GST Calculator
Reverse GST Calculator NZ 🇳🇿
The Reverse GST Calculator helps you determine the GST-exclusive amount and GST component from GST-inclusive prices in New Zealand. This is particularly useful for businesses, accountants, and individuals who need to separate GST from their total prices.
How It Works
New Zealand applies a 15% GST rate to most goods and services. This calculator uses the reverse calculation method:
- Amount Ex GST = GST Inclusive Amount ÷ 1.15
- GST Amount = GST Inclusive Amount – Amount Ex GST
Example
If you have a GST-inclusive price of NZD 115.00:
- Amount Ex GST = 115.00 ÷ 1.15 = NZD 100.00
- GST Amount (15%) = 115.00 – 100.00 = NZD 15.00
You can add multiple amounts using the “Add Row” button to calculate totals for multiple items at once.
Worked Examples
A retailer in Napier buys a display fridge for $2,875 including GST and needs the GST-exclusive cost for her books. Amount ex GST = $2,875 ÷ 1.15 = $2,500.00. GST amount = $2,875 − $2,500 = $375.00. She claims $375 of GST in her next return.
An invoice arrives for $575 including GST. Amount ex GST = $575 ÷ 1.15 = $500.00, so the GST is $75.00. A quick check with the 3/23 rule gives the same answer: $575 × 3 ÷ 23 = $75.00.
A third check uses everyday numbers. A $1,150 invoice divides to $1,000 ex GST with $150 of GST, and a $460 receipt divides to $400 ex GST with $60 of GST. Once you see the pattern, spotting an invoice error gets much easier.
When To Use The Reverse Calculation
Use the reverse calculation whenever a price already includes GST and you need the split: entering supplier invoices into your accounts, working out the GST you can claim back, or comparing a GST-inclusive shelf price with a GST-exclusive trade quote. It only works where the full price carries the standard 15% rate.
Reverse GST Calculator FAQs
What is reverse GST?
Working backwards from a GST-inclusive price to find the price before GST and the GST component. See the GST formula NZ page for all three formulas.
Why divide by 1.15 instead of subtracting 15%?
Because 15% of the GST-inclusive price is more than the GST inside it. For $115, subtracting 15% gives $97.75, which is wrong. Dividing by 1.15 gives the correct $100.
What is the 3/23 rule?
A shortcut for the GST component: multiply the GST-inclusive price by 3/23. For $230, that is $30 of GST. The guide to removing GST from prices explains both methods.
How do I check my answer?
Multiply the ex-GST amount by 1.15. If you land back on the original inclusive price, the split is right. For example, $2,500 × 1.15 = $2,875.
Can I use this for zero-rated or exempt sales?
No. The reverse calculation assumes the standard 15% rate. Zero-rated supplies use 0% and exempt supplies carry no GST.
