Mortgage indexation in Portugal normally ties your loan rate to a benchmark (most often Euribor) plus a fixed bank margin, and the contract sets how often the rate is updated (monthly, quarterly, six-monthly, etc.). If your mortgage updates every six months, your monthly payment is recalculated twice a year when the benchmark changes, so borrowers should check the reference rate, the bank margin, and whether the contract changes the payment amount or the loan term.