When you log on to the SKAT website using your NemID, you can see your preliminary income assessment. This shows you the income SKAT expects you to have in the next year, and this estimated income is the basis for your tax rate.
You should view the preliminary income assessment as a tax budget of your income for the coming year. It is an estimate of your income, which is used to calculate how much tax you have to pay.
This estimate is based on your tax assessment notice of the previous year.
If your income changes substantially, you can correct your preliminary income assessment so that you pay the correct amount of tax. That way you avoid getting a large tax bill at the end of the tax year.
Find more information from SKAT