Actualité - Unilateral promise to sell vs. bilateral sales agreement: what are the

Article updated on 09/10/2026

In France, when a seller and a buyer reach an agreement, the sale is not completed in a day: a preliminary contract comes before the final deed. Unilateral promise or sale agreement, what are the differences? Optimhome explains.

Key points

The unilateral promise to sell commits only the seller; the buyer holds an option that they may or may not exercise.
The sale agreement commits both the seller and the buyer: it “amounts to a sale” (article 1589 of the Civil Code).
Immobilisation indemnity (promise) or security deposit (sale agreement): generally 5 to 10% of the price.
In both cases, conditions precedent protect the parties and the buyer has a 10-day cooling-off period.

Update of 9 October 2026
2026 reminder: the technical diagnostic file, which includes the DPE energy performance certificate and, for the most energy-intensive houses, the energy audit, must be appended to the promise or the sale agreement (article L. 271-4 of the French Construction and Housing Code). The audit must even be given to the buyer from the very first viewing. If it is missing or contains errors, the buyer can request it before the final deed is signed, or even invoke a breach of the seller’s duty to inform.
Source: Le Mag Juridique ; Kohen Avocats, 2026.

Sale agreement: preliminary contract and final deed

When the seller and the buyer reach an agreement on the sale, a preliminary contract is generally drawn up before the signing of the final deed. This preliminary contract sets out the mutual agreement between the seller and the buyer and defines the precise conditions of the sale of the property.

Conditions precedent in the preliminary contract

The preliminary contract may include conditions precedent, which settle uncertainties related to the sale, such as the municipality’s or the tenant’s right of pre-emption, obtaining a bank loan, or a building permit.

Sale agreement and promise to sell: two types of preliminary contracts

The Unilateral Promise to Sell Article 1124 of the Civil Code states that “A unilateral promise is the contract by which one party, the promisor, grants the other, the beneficiary, the right to choose to conclude a contract whose essential elements are determined, and for whose formation only the beneficiary’s consent is missing.”

The unilateral promise to sell commits only the owner, who reserves the property for a prospective buyer at a set price for a limited period. The buyer can then decide whether or not to buy the property.

In return, the buyer pays an immobilisation indemnity generally between 5 and 10% of the sale price. If the buyer decides to exercise the option, the owner is obliged to sell. If the option is not exercised, the indemnity is kept by the owner.

When signed privately (without a notary), this promise must be registered with the tax office within 10 days of its acceptance by the beneficiary, or it is void. If it lasts more than 18 months, it must be concluded by notarial deed.

The sale agreement (compromis de vente)

Article 1589 of the Civil Code specifies that “A promise to sell amounts to a sale when there is mutual consent of both parties on the thing and on the price.”

Unlike the unilateral promise, the sale agreement commits both parties. It is signed when the seller and buyer are certain they want to complete the sale. The sale agreement includes a security deposit, generally between 5 and 10% of the sale price, but does not require registration with the tax office.

Conditions precedent and their purpose

Whether in a promise to sell or a sale agreement, conditions precedent can be included to provide for the preliminary contract to become void if they are not met. The buyer obtaining a loan is the most common condition precedent. If the loan is refused, the sums paid are returned to the buyer.

Consequences in the event of death

Unilateral Promise to Sell: The death of the promisor after signing does not call the obligations into question; they pass to the heirs. If the beneficiary dies before exercising the option, their heirs will decide what to do next.

Sale Agreement: The seller’s death transfers their obligations to their heirs. If the buyer dies, their heirs must honour the commitments made, unless otherwise stated in the preliminary contract.

Penalties if the sale does not go through

Unilateral Promise to Sell: If the buyer exercises the option and the promisor refuses to sell, the buyer can seek enforcement of the sale or claim compensation. If the buyer does not exercise the option, the immobilisation indemnity is kept by the owner.

Sale Agreement: If one of the parties withdraws from the transaction, the other can seek enforcement of the sale or claim compensation.

The buyer’s right of withdrawal

The Macron law of 6 August 2015 extended the cooling-off period for non-professional buyers of a home to 10 days. The buyer can go back on their commitment without justification during this period, by giving notice of withdrawal by registered letter with acknowledgement of receipt or by any other means offering equivalent guarantees (hand delivery against receipt, bailiff).

Conclusion

Drawing up a preliminary contract is a crucial step in a property sale, clarifying commitments and including conditions precedent to secure the transaction. Whether a unilateral promise to sell or a sale agreement, these contracts define the parties’ responsibilities and offer protection if the sale does not go through.