After you have submitted your Dutch tax return, you will receive a preliminary assessment from the tax authorities. In case you were invited by the tax authorities to submit your return before May 1, and you have filed your return before April 1, you will receive notice from the tax authorities before July 1. For returns filed after April 1, you will receive a notice after 10 to 12 weeks. If your tax return was submitted with either a C or an M form, it may even take up to 24 weeks or more.
Initially you will receive a preliminary assessment from the tax authorities, which is based on the tax return, but without being checked by the tax authorities. Once they have checked the return, a final assessment will follow.