One type of mortgage in the Netherlands is a "banksparen" ("bank savings", the word isn't very descriptive) mortgage.
It is designed to make maximum use of tax laws: instead of paying down the mortgage, you put money on a savings account at the same bank that pays the same interest rate as is owed on the mortgage, and that can only be used to eventually pay off the mortgage. In the meantime one still pays full interest on the mortgage (that can be deducted from income for income tax) while the money in the savings account is exempt from wealth tax as long as it will be used for paying off the mortgage.
New mortgages of this kind are not tax deductible anymore since 2013 or so (and so they're not offered anymore), but I have an existing one at ABN Amro.
To qualify for the tax exempt status of the savings account, there are strict rules -- money has to be paid into the account yearly for at least 15 years, the lowest amount and the highest amount paid may not differ by more than a factor 10 and the resulting sum has to be used to pay off a mortgage in the end.
Are there any special rules when paying off the mortgage before the end of those 15 years, for instance when selling the house to buy a new one?
If the answer is no, and one has to keep the savings account, is it possible to pay off the mortgage and get another one, eventually using the savings to pay off that one?
If yes, what will the interest rate on the savings account be, considering that it's tied to the rate of the mortgage now?