Briefing
According to the published interbank fixings from the Euriboradministrator and monthly averages calculated from these figures, the provisional monthly average for the 12-month Euribor for September 2026 is around 3.22 per cent. These monthly averages are calculated as the arithmetic mean of the daily Euribor fixings supplied by the European Money Markets Institute (EMMI) / Eurosystem. Daily rate movements during the month mean that the fixings published so far put the monthly average in the range of 3.21–3.23 per cent.
For borrowers in Spain the key factor is which reference rate is specified in their contract: many variable-rate mortgages link their interest-rate adjustments to the Euribor monthly average for the same month, which is incorporated by the Banco de España into the official reference tables and becomes the basis for contractual adjustments once published in the Boletín Oficial del Estado (BOE). In practice, a Euribor rise of around 0.27 percentage points compared with August 2026 means that the next payment will increase noticeably for each household subject to an annual review; the exact additional cost depends on the outstanding balance, contractual margin (spread), term and adjustment method set out in the contract deed. Banks must inform borrowers in good time about interest-rate changes; the legal basis for publishing the official reference indices and using them in mortgage contracts is set out in the relevant regulations and the publication practices of Banco de España and the BOE.
Until the monthly figure is formally published in the BOE, the September average should be treated as provisional. In practical terms, affected households should check their loan documents, confirm the reference month stipulated in their contract and, if necessary, discuss repayment or payment-deferral options with their bank. More precise figures for the actual impact on individual contracts can only be reliably calculated after the official entry in the BOE.
Editor: Daniel Mayer (Article created with AI assistance).