In determining how much tax you have to pay for an entire year, it does not matter how many jobs or employers you have. The Dutch Tax Office only looks at the amount of your total annual income.
Payroll tax
A second job means a second income with a second employer. With each paid job, you must pay payroll taxes. Payroll tax is the collective term for taxes and contributions deducted from your gross salary. This is where it gets fun, because on one of the two jobs, you can get payroll tax credits, and it is up to you to decide which one of them. If you choose payroll tax credits on the job that earns you the most, then practically speaking, you will also receive more deductions in euros. How much wage tax credit is deducted from taxes depends on how much you earn.
End-of-the-year refund
With a second job, due to the elimination of the wage tax credit, it initially seems as if you must pay more tax than with your first job. In principle, your second income is taxed more heavily during the year than when you have one income. However, only at the end of the year is the balance sheet drawn up. The tax authorities lump everything together at the end of the year. Any overpaid tax is then simply refunded to you when you file your tax return. So, you can think of the payroll tax as a piggy bank. If your income from a second job exceeds €36,650, you may also be entitled to more tax credits.