If you want to claim an interest discount (reduction of interest surcharge), you must increase the value of the home with a validated valuation report. If you have a mortgage of 50/67/80/90% of the value, you can get a lower mortgage interest than when you took out the mortgage for, for example, 100% of the value. If you have been living in your current home for a few years or if you have renovated or modernized it, the value may have increased enough to be entitled to lower interest. Or do you want to transfer the mortgage? Or do you have a bridging mortgage on your current home to finance your new home? Then you also need an appraisal to determine the current value.