Capital Gains Tax
New Zealand has no tax on capital gains.
If, however, you buy and sell property frequently, your gains will be taxed as income.
If you buy and sell stocks and shares frequently, it may be that the Inland Revenue Department (IRD) will class your activity as "trading" rather than "investing". If this is the case, you will be liable to pay tax on your trading gains as if they were income. You will also be able to offset losses and fees on your share dealings against tax and also deduct expenses such as computers, software books etc that you use for your share trading from your taxable profits.
The IRD uses your intention when you buy a stock as their guide to whether you are a trader or investor. If you wish to avoid paying capital gains tax, it can be useful to write down your reasons for buying and selling any particular stock as evidence that you are an investor rather than a trader.
For example, an investor might record that he bought a stock for the purpose of receiving a growing dividend income and sold it to preserve his capital.
Note - the above information is of a very general nature and is not intended to be used as the basis for any financial decisions you might make. If you require tax or financial advice, please ensure you consult a qualified tax professional.