Learn about rates and methods for converting overseas currency to New Zealand dollars, and when to use them.
When to convert currency
You need to convert overseas currency to New Zealand dollars to work out your income tax and GST.
Generally, you can choose how you convert overseas currency. There are some exceptions, for example:
- financial arrangements rules
- foreign investment fund (FIF) rules
- controlled foreign company (CFC) rules.
In these cases, you must use the methods and rates specified for each type of arrangement and transaction.
Read more in the Guide to foreign investment funds – IR461 and in Determination G9A on the Tax Technical website.
Foreign investment funds (FIFs)
Determination G9A: Financial arrangements (taxtechnical.ird.govt.nz)
Using exchange rates and methods
You can use foreign exchange rates:
- that we have published for specific types of arrangements or transactions
- from the Reserve Bank of New Zealand
- from other countries’ central banks
- another rate that’s appropriate given the nature of your transaction.
It’s important to use the same exchange rate sources and methods consistently over time. If you must change the rates you’ve been using (because of a software change for example), keep a record of the reasons for the change.
Rates
For conversion methods, you can use the mid-month, end-of-month or rolling average rate. Use these methods when they’re appropriate to your situation.
The following rates are from the Reserve Bank of New Zealand. You can download the file for the year you need or find more information on the Reserve Bank website.
Exchange rates and the Trade Weighted Index (rbnz.govt.nz)
Rolling 12-month average rates
Each rolling 12-month average rate is the average of the mid-month rates for the last 12 months. The rolling average rate shown for March is useful for people with standard balance dates.
If you have a lot of repeated transactions during the tax year, it’s usually appropriate for you to reduce compliance costs by using this average rate across those transactions. Do not use it to convert significant and one-off transactions.
This is 1 of the methods that you can use to calculate FIF income under most FIF calculation methods. If you start using this method to calculate FIF income, you must keep using it every year.
Mid-month rates
For most purposes, we accept the mid-month rate as the equivalent of the actual rate on any day in that month.
Past years' rates
‘Rolling 12-month average rates’ contains mid-month rates before May 2026.
End-of-month rates
This rate is useful when you need to convert a market value or balance at the start or end of the tax year. The rate on 31 March can also be used as the rate on 1 April.
Using other rates and methods
You can use your own rates and methods for converting currency. For example, to fit with your accounting software or reduce your costs.
Make sure your rate is appropriate for your transaction type. For example, do not use cash or foreign cheque rates.
Use the same source of rates for all your overseas currency amounts. Do this consistently over time.
Keep records of the source, type and date of the exchange rates you use your calculations.
More information
Determination - Foreign currency approval FX 21/01 (taxtechnical.ird.govt.nz)