If you use Airbnb to provide short-term accommodation in your house in which you also live, the IRD’s “mixed-use asset (holiday home)” rules don’t apply and guests are not classed as boarders. Except when you list a whole house which is vacant for 62 days each year, mixed-use asset rules do apply and calculations differ from those for homes where the hosts also live.
Anything you spend as an Airbnb service provider may be claimed as an expense. For shared expenses, like power and internet, claims need to be fair and reasonable.
You can claim some home utilities, rates, insurance, and interest – and all food and other consumables that guests use. You can also claim depreciation on chattels and appliances used by guests only. You can claim some depreciation on other shared chattels and appliances, like claiming a portion of utilities.
If you spend money to keep your property attractive for guests, you can claim some of those costs. You will most likely have to apportion those expenses.