Short answer
A consumer can challenge a standard loan or mortgage term under Directive 93/13/EEC (the Unfair Contract Terms Directive, or UCTD) if it was not individually negotiated and, contrary to good faith, causes a significant imbalance. Even a term defining the loan's main subject matter—such as repayment in a foreign currency—escapes unfairness review only if transparent. The consumer must have been able to understand the mechanism and assess its potentially significant financial consequences when contracting.
For foreign-currency loans, key evidence is what the bank explained about exchange-rate volatility and its effect on instalments and principal. For a variable-interest clause, courts examine the index and adjustment mechanism, accessibility of information, official warnings and comparable market methods and rates. An official index is not automatically fair.
If a clause is unfair, it is not binding. Whether the agreement survives, and what each side must repay if it does not, are national-law questions constrained by the UCTD's effectiveness and deterrent purpose. Procedure must permit effective review before enforcement causes irreversible loss. The Mortgage Credit Directive adds safeguards, but generally does not apply to agreements already existing before 21 March 2016.
Start with the UCTD test
The UCTD applies to contractual terms between a professional lender and a consumer acting outside a trade or profession. A genuinely individually negotiated term falls outside Article 3, but using a pre-drafted agreement usually points the other way; the lender bears the burden if it says the term was individually negotiated.
The court assesses circumstances known or reasonably foreseeable when the contract was concluded and the agreement as a whole. Under Aziz, significant imbalance is tested against the consumer's position under national law without the term. Good faith asks whether a fair lender could reasonably expect individual acceptance.
Terms concerning the main subject matter or price are excluded from substantive review under Article 4(2) only insofar as they are in plain, intelligible language. Member States may provide stronger protection and permit broader review.
“Member States shall lay down that unfair terms used in a contract concluded with a consumer by a seller or supplier shall ... not be binding on the consumer.” —
National courts must examine possible unfairness of their own motion once they have the necessary law and facts. A consumer should still identify the disputed clause, pre-contract information, payment history and remedy sought.
Foreign-currency loans: could the consumer understand the real risk?
A repayment-in-foreign-currency term may define the main subject matter because it characterises the loan. That does not end the analysis. In Kásler, the Court held that the consumer must be able to understand the conversion mechanism and its relationship with other terms, and evaluate the resulting economic consequences using clear criteria.
Andriciuc applied that standard to exchange-rate risk:
The borrower must be able to assess “the potentially significant economic consequences” of the foreign-currency term for the borrower's financial obligations. —
A statement that rates may fluctuate is not necessarily enough. The court asks whether the information enabled an average, reasonably informed, observant and circumspect consumer to decide prudently. Relevant material includes scenarios, depreciation's effect on payments and capital, the consumer's income currency, and the bank's knowledge of possible variations. The lender is not strictly liable whenever a currency later moves adversely; the inquiry concerns transparency and risk allocation at conclusion.
Different buying and selling exchange rates may also be challengeable. Kásler requires the agreement to reveal how conversion works. If deletion would invalidate the agreement and especially harm the consumer, a court may exceptionally substitute a supplementary national rule—not merely preserve the lender's economics.
Variable rates and official reference indices
An interest clause should disclose what changes the rate, how often, the margin and payment effect. For covered loans, the Mortgage Credit Directive also requires reference rates to be clear, accessible, objective and verifiable, with historical records maintained.
In Kutxabank, concerning Spain's IRPH mortgage index, the Court held that official publication of an index's definition and earlier values can contribute to transparency if the lender gives indications making that material sufficiently accessible. If it does not, the lender must provide the definition and relevant information itself, including an important official warning about the index's features and consequences.
An official index does not by itself establish the lender's good faith; the court must consider transparency, the calculation method, the resulting rate and comparable market rates at the date of the loan. —
A term reflecting a mandatory provision may fall outside the UCTD under Article 1(2). But choosing an available official index is not automatically mandatory. Nor do potentially unfair components in the index make the borrower's clause automatically unfair. The term, disclosures and economic imbalance still require assessment.
What happens after a term is found unfair?
The starting point is non-application, restoring the position that would have existed without the term. A court generally may not revise it, because that would weaken deterrence. The contract continues if it can operate without the term and the consumer does not prefer invalidity's protection.
If the agreement cannot survive, national law governs invalidity and restitution, but cannot neutralise UCTD protection. In Bank M, which concerned an invalid foreign-currency mortgage, the Court ruled that the bank may not obtain compensation beyond repayment of the capital advanced plus statutory default interest from notice. Such lender remuneration would remove the deterrent effect. The Directive did not categorically bar additional consumer claims where national law permits them and proportionality is respected.
Herchoski (C-902/24) permits alternative set-off of the bank's principal claim, provided it is not due before judicial invalidity and costs do not deter the consumer. UniCredit Bank and Momentum Credit (C-679/24) rejects a five-year period from contract conclusion where the consumer could not know of unfairness, and using a later CJEU or national supreme-court ruling to start or resume it. Claims, interest and dates remain national-law matters.
Mortgage enforcement must allow an effective challenge
Acceleration, default-interest and enforcement-cost terms are reviewable under the same UCTD framework. For acceleration, relevant matters include the seriousness of the breach compared with the loan's amount and duration, departure from default national law, and whether the consumer has an effective way to cure or contest the breach.
Procedure cannot make the substantive protection illusory. Aziz concerned a system in which unfairness could not be raised in mortgage enforcement and the court hearing a separate action could not stay the sale:
The UCTD precludes such rules where interim relief, including a stay of enforcement, is necessary to guarantee the full effectiveness of the court's final decision. —
Finality matters only after effective review. Ibercaja Banco held that an unexplained order stating no unfair terms existed could not bar later review where the consumer had not been told silence would make it final. After sale and third-party transfer, the sale may stand if the consumer retains a compensation route.
For mortgages governed by Directive 2014/17/EU, Member States must encourage reasonable pre-foreclosure forbearance, limit default charges to creditor compensation, seek the best obtainable foreclosure price and facilitate repayment of remaining debt. Those duties do not decide whether a term is unfair.
The Mortgage Credit Directive's scope and limits
Directive 2014/17/EU mainly covers consumer credit secured on residential immovable property and credit used to acquire or retain rights in land or a building, subject to its exclusions. It requires creditworthiness assessment and standardised pre-contract information.
For foreign-currency loans, Article 23 requires Member States to provide either a right to convert into an alternative currency or another arrangement limiting exchange-rate risk. Unless risk is already capped below that level, the creditor must warn the consumer regularly when exchange-rate movement causes the outstanding amount or instalments to differ by more than 20% from what the contract-date rate would produce. The warning must explain the available conversion right or risk-limiting mechanism.
These protections are not retrospective. Article 43 excludes agreements existing before 21 March 2016. An older mortgage may still be challenged under the UCTD and national law, but does not acquire the later Directive's rights solely from Directive 2014/17. For later agreements, compliance is important evidence, not automatic proof of fairness.
Conclusion
The strongest challenge identifies a specific standard term and reconstructs what an ordinary consumer could understand at the date of contracting. Foreign-currency cases turn on intelligible disclosure of potentially severe exchange risk; variable-rate cases on the index, adjustment mechanism, warnings and market comparison; enforcement cases on proportionality and access to timely judicial protection.
An unfair term is not binding, but the consequences are not identical across Member States. Contract survival, restitution, interest, limitation and the effect of a completed property sale depend on national law subject to the UCTD's requirements of effectiveness and deterrence. The Mortgage Credit Directive adds valuable safeguards for covered, generally post-21 March 2016 mortgages, but does not replace the unfair-terms analysis.
Sources
This article provides general legal information, not advice for a specific matter. Laws, facts and procedural deadlines may change the result. Follow the linked primary sources and obtain local advice before acting.