Whether you arrived in or left the Netherlands, a migration income tax return can be a fun tax return to file. The fun is in the tax refund. Your Dutch employer withheld tax on your salary as if you would have stayed the full year in the Netherlands. As that clearly was not the case, too much tax has most likely been withheld and you can claim that back.
If you are making use of the 30% ruling, neither you nor your Dutch tax partner need to report your worldwide wealth. However, you do need to let the tax office know that you want to make use of this rule. Neither your Dutch or foreign assets will have to be reported, with the exception of a possible second home you own in the Netherlands.
Not everybody can make use of the 30% ruling. This means that you will be taxed as native Dutch people are taxed. You will also need to report your worldwide assets. This is not always understood or feared.
Our experience teaches us that many internationals have property abroad with rental income. They wonder how much of this rental income is taxed, but rental income is not taxed. This is due to dual taxation treaties. Some internationals build up pension rights abroad. Most pension rights are not part of the Dutch wealth tax return, however, some are. You will first need to reach the pension date to actually be able to benefit from it. That said, pension income is taxed in Box 1, like your salary income, this includes foreign pension. The exception is a foreign state pension.
Internationals abroad sometimes use trust funds as a way to protect family assets. The concept of trust funds is not accepted in the Dutch income tax return. Your tax advisor will look at the trust fund and if you are the actual current beneficial owner of the assets, you need to include that part of the trust fund in your Dutch income tax return.
If you are self-employed and registered with the Dutch chamber of commerce, you are obliged to file your income tax return. Via this income tax return, you are also charged the health care premium employers pay for their employees. As you have no employer, this healthcare premium is payable by you.
If you are no longer a Dutch tax resident, why file an income tax return? Of course, if you own property in the Netherlands, you need to file an income tax return in the Netherlands. This could be one reason. Note that rental income is not taxed. So, you can keep an empty property or an occupied home. Regardless, you are meant to file a Dutch tax return based on the locally determined value.
You own the house that is your main residence. Via the income tax return, you can claim the mortgage costs. You earned royalty income, or other income that is neither employment income nor salary income. This income is subject to Dutch taxation. Hobby income is not a source of income unless you are able to prove the tax office wrong and have a hobby that is a source of income. But often a hobby costs more than it yields.