When you are already repaying a loan on a rental apartment and wish to buy a second property, the way the bank calculates your debt-to-income ratio changes everything. Two methods coexist in the French banking landscape, and one of them, the differential calculation, can turn a rejected application into an accepted one. Understanding this mechanism allows you to target the right institutions and prepare a suitable application.
Positive rental balance and debt-to-income ratio: the mechanics of the differential
Let’s take a simple example. You earn 3,000 euros net salary, you repay 700 euros per month for a rented studio, and this studio brings you 900 euros in rent.
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With the classic method, the bank adds up all your income (salary + weighted rents) on one side, and all your credit charges on the other. The rent received is often reduced by about 30% to account for the risk of vacancy. This approach mechanically inflates your debt-to-income ratio.
With the differential calculation, the bank reasons differently. It first subtracts the monthly payment of the rental loan from the rents received. If the balance is positive, it adds to your income. If the balance is negative, only this deficit weighs on your charges. The differential isolates the rental operation from the rest of your budget.
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The concrete result: your debt-to-income ratio can drop by several points, freeing up borrowing capacity for a new project. To identify the banks using the differential calculation, one must first understand that the situation has evolved significantly since the recommendations of the HCSF.
HCSF Recommendations and the Decline of Differential Calculation in Banks
The High Council for Financial Stability (HCSF) has gradually tightened its recommendations on calculating the debt-to-income ratio. The 35% ceiling (including insurance) has become the norm, and the classic method has established itself as the reference in most institutions.
Most major network banks have abandoned the differential calculation to comply with these recommendations. The differential is not prohibited by law, but its use has significantly decreased. A few regional banks and some institutions specialized in rental financing continue to apply it on a case-by-case basis for profiles of experienced investors.
Banks that maintain this method do not openly advertise it. They use it as a commercial lever to attract applications from wealth management investors, often in exchange for income domiciliation or investments.
Personalized stress simulations: the strategy of rental investors
In light of the decline of the differential, some investors try to convince their bank to think differently. The technique involves presenting an application accompanied by personalized stress simulations that demonstrate the financial solidity of the rental operation.
In practical terms, this means providing:
- A detailed forecast table outlining the rents received, actual charges, and net cash flow across several scenarios (two months of vacancy, rent decrease, rate increase)
- A rental history proving the absence of unpaid rents and a high occupancy rate on properties already owned
- A projection of net worth showing that overall debt remains controlled, even in the event of a market downturn
The goal is to show that the actual risk is lower than the theoretical risk calculated by the classic method. Some banks agree to requalify the application on this basis, without formally calling it “differential calculation.”
Risks of Regulatory Requalification
This approach carries a risk. The HCSF monitors the practices of institutions, and a bank that grants too many loans exceeding the 35% threshold risks being reprimanded. Banks have a margin of exemption (about 20% of their quarterly production can exceed the criteria), but this margin is regulated and primarily reserved for the purchase of primary residences.
An investor obtaining financing through this strategy does not run any personal risk. The regulatory risk falls on the bank, not on the borrower. This explains why institutions remain cautious and selective.
Transfer of mortgage: retaining an inherited differential
A rarely exploited lever concerns the clauses for transferring a mortgage. According to the ANIL guide on the transfer and renegotiation of rental loans, a borrower can retain the initial calculation conditions of their old loan if the rental balance remains positive.
In practice, if you obtained a loan at a time when differential calculation was common, and your contract includes a transfer clause, you can transfer this loan to a new property. The inherited differential from the initial contract then remains applicable.
This option assumes two conditions:
- That the original loan contract explicitly contains a transfer (or transferability) clause
- That the new property generates a positive rental balance, meaning that the rents at least cover the monthly payments of the transferred loan
- That the bank accepts the new property as collateral, which involves an appraisal and analysis of the local market
Few investors think to check this clause in their old contracts. For those holding loans signed before the tightening of the HCSF recommendations, this is a priority avenue to explore.
The differential calculation has not disappeared from the banking landscape, but it has shifted. It is now negotiated on a case-by-case basis, often through a specialized rental investment broker, and sometimes under a different form than its historical name. Checking the transfer clauses of your old loans and preparing solid stress simulations remains the best way to access this more favorable calculation method.