The interest rate is linked to the fluctuation of a reference financial index, generally the Euribor. Based on the trend of the financial market, the outcome of the calculation of the mortgage installment can vary: upwards when the Euribor rises, downwards when the index falls. This means that the amount of the installment, in mortgages with variable rates, will depend on the market trend referring to the period envisaged for the payment of the new installment.