Having processed your tax filing, the tax authority will inform you in detail about your tax liability.
If you have filed prior to 1 April, you can expect to hear about your tax assessment (belastingaanslag) no later than 1 July. There may be grounds to formally object to the assessment (bezwaar indienen) in which case you will need to detail your objection – usually with supporting explanation and/or evidence – and request to the tax authority to reconsider your assessment based on the new information.