Kosten koper (k.k.) are the one-off costs a buyer pays on top of the purchase price, including transfer tax (overdrachtsbelasting), notary fees, mortgage advice and the valuation report (taxatierapport). They typically come to a few percent of the price and are paid from your own money, not the mortgage. Existing homes are usually sold “kosten koper”, while new-build is sold “vrij op naam” (VON).