The interest rate applied to the fixed rate mortgage, i.e. the nominal rate, is given by the sum of the reference index for this type of loan, i.e. the Irs (or Eurirs), and the spread, i.e. the increase applied by the bank as its profit margin.
Once their value has been established in the loan agreement, both will remain unchanged until the end of the loan, therefore the interest rate will also remain fixed.
If the spread is established by the individual banking institution, the IRS is instead determined daily by the European Banking Federation, based on the expectations of the financial markets.
There is no single IRS rate, but the one relating to the length of the single home loan must be chosen: for a 5-year loan, the bank will consider the IRS 5 years, for a 20-year loan the IRS 20 years. There are Irs for all main terms, from 1 to 50 years.
In summary, therefore, a mortgage that lasts 15 years will have an interest rate made up of 15-year Irs spread, while one that lasts 30 years will have a rate made up of 30-year Irs spread, and so on.
In addition to the interest rate, the type of monthly payment must be chosen, which can be constant, increasing or decreasing.
Each installment always consists of a capital share and an interest share, in variable proportions depending on the case, but it is important to reiterate that all amounts are defined from the beginning of the mortgage.
The constant installment is by far the most widespread, according to the "French" amortization plan: in the case of a fixed-rate loan and constant installment, the sum to be repaid to the bank is divided into all equal monthly amounts, with the principal which grows progressively, while the interest rate decreases accordingly.
The decreasing installment, or "Italian-style", is instead given by a constant principal quota and an interest quota which decreases over time.
Finally, the increasing installment provides for an increasing amount on the basis of deadlines established by contract.