Both flow into a single income-tax assessment. The freelance income stacks on top of your salary and is taxed at your top marginal rate — not from zero.

For example, a €65,000 salary plus €25,000 of freelance work triggers about €9,422 of additional income tax for the year. Set that share aside per invoice.

No. Under the predominant-activity rule, only your main activity bears health and long-term care insurance. With a salaried main job, your freelance side income is KV/PV-free.

Because no tax is withheld at source on your freelance income. The tax on it only falls due at assessment — as a back-payment (Nachzahlung).

Usually yes: if the expected back-payment exceeds a small threshold, the Finanzamt sets quarterly prepayments. That spreads the burden and avoids one large bill.

Health and long-term care insurance is levied once, by your predominant activity — not twice. With a salaried main job the side income is contribution-free; if self-employment predominates, KV/PV is assessed on a combined base.