Debt capacity & remaining-budget simulator
Simulator — Debt capacity
Gauge how sustainable a loan really is — ratio and remaining budget. See also: PEA vs brokerage account.
Debt capacity is not just a regulatory percentage. The debt-to-income ratio — capped at 35% by France’s HCSF for most mortgages — is a ceiling, not a target: necessary but not sufficient. Two households at the same ratio can be very differently exposed; what separates them is the remaining budget, income stability and the structure of fixed costs. The simulator below puts both side by side: the ratio everyone looks at, and the remaining budget that actually decides whether the situation holds.
The ratio says "yes" — your remaining budget says whether you hold
The debt-to-income ratio (HCSF cap 35%) is necessary but not sufficient. At an equal ratio, it is the remaining budget that separates a robust situation from a fragile one.
Budget-structure observation, non-predictive · assumptions entered by the user · the HCSF 35% cap is a regulatory reference, not an approval threshold · Eco3min — educational tool, neither advice nor a recommendation.
Output from a simplified model, depending solely on the assumptions entered. The HCSF 35% cap is a regulatory reference, not an approval threshold: a lender’s decision rests on other criteria too. Neither advice nor a personalized recommendation.
The debt-to-income ratio: a ceiling, not a target
The debt-to-income ratio divides total loan payments by net income:
Debt-to-income = (total loan payments) ÷ (net income) × 100
Since 2022, France’s HCSF (High Council for Financial Stability) caps this ratio at 35%, insurance included, for most mortgages — with a limited, framed flexibility margin for a minority of files. The cap protects borrower and banking system alike. But it only says how much of income goes to repayments; it says nothing about what is left to live on. The debt-to-income principle itself is general, even where the specific 35% figure is French.
Remaining budget: what the ratio hides
The remaining budget is what is left once loan payments are made: remaining budget = net income − loan payments. That figure, divided by household size, measures real resilience. The same ratio can hide opposite situations:
| Household | Income | Payments | Debt-to-income | Remaining budget |
|---|---|---|---|---|
| A (1 person) | €2,000 | €680 | 34% | €1,320 |
| B (4 people) | €6,000 | €1,800 | 30% | €4,200 (€1,050/person) |
| C (4 people) | €3,000 | €1,000 | 33% | €2,000 (€500/person) |
Household C, below the cap at 33%, is more fragile than B at 30%: €500 per person versus €1,050. The ratio alone would rank them the same. That is why the simulator shows the remaining budget per person and places it against the HCSF cap — the regulatory marker and the real margin, together.
Example: a €200,000 loan over 20 years
For a two-person household, €3,000 net income, no existing loans, borrowing €200,000 at 3.5% over 20 years: the payment is about €1,160, a debt-to-income ratio of 38.7% — above the HCSF cap. The remaining budget is still €1,840/month, i.e. €920 per person. Extending the term or lowering the amount brings the ratio back under 35%; the simulator lets you test each lever and see its effect on the remaining budget.
What the simulator does not do
It does not try to maximize a borrowing amount and does not prejudge a lender’s decision. It excludes borrower’s insurance, other fixed costs (energy, childcare), taxes and future income changes. It lights up a budget structure at a point in time and its vulnerability to a shock — a rate rise on a variable loan, an income drop, a lasting rise in costs.
Frequently asked questions
How do you calculate your debt-to-income ratio?
Divide total loan payments (existing + planned, mortgage and consumer) by net monthly income, times 100. The simulator above computes it and places it against the HCSF 35% cap.
Is the 35% cap mandatory?
It is the HCSF rule for most French mortgages since 2022, insurance included. Banks keep a framed flexibility margin for a minority of their output. It is not an approval guarantee: a file below 35% can be refused, one above accepted within the margin.
What is the remaining budget?
It is what is left of income once loan payments are made, to cover everything else. Divided by household size, it measures real resilience far better than the ratio alone.
Why aren’t two households at the same ratio equivalent?
Because 30% of €6,000 leaves far more to live on than 30% of €2,000. The ratio is relative; the remaining budget is absolute. That’s the difference between a manageable constraint and a stifling one.
Key takeaways
- The debt-to-income ratio (HCSF 35% cap) is a ceiling, not a target — and not an approval guarantee.
- The remaining budget, especially per person, measures real resilience better than the ratio.
- At an equal ratio, one household can be robust and another fragile.
- The tool lights up a budget structure; it does not maximize a loan or replace a lender’s analysis.
Go further
Structure all your flows → the personal budget management tool. Measure what inflation removes from a return → the real return after inflation calculator.
Last updated — 28 May 2026
Disclaimer – Financial Information: The analyses, commentary, and content published on eco3min.fr are provided for informational and educational purposes only. They do not constitute investment advice or a solicitation to buy or sell financial instruments. Past performance is not indicative of future results. All investment decisions involve risk and are the sole responsibility of the reader.