Business taxation: Taxes, deductions and optimization

Corporate tax optimization rarely starts with a scheme. It starts with three structural decisions — the tax regime, the treatment of investments, and the rigor of supporting documentation — which determine most of the actual tax burden. Everything else is marginal adjustment, often overrated. This article covers these three areas, then the points where the tax authorities most frequently make adjustments.

The tax regime, a foundational decision

Profits are taxed either under personal income tax in the hands of the operator or partners, or under corporate income tax at the level of the business itself.

The applicable regime depends on the legal form, but it is largely optional: a sole proprietorship or a partnership can elect to be taxed under corporate income tax, and certain capital companies may, subject to conditions and for a limited period, elect the partnership tax regime.

The trade-off hinges on one concrete point: what the manager actually withdraws. Under personal income tax, the entire profit is taxed in the manager's hands, whether withdrawn or not. Under corporate income tax, undistributed profit is taxed only at the company level; compensation paid is deductible from taxable income, and dividends follow their own regime. A business that reinvests generally benefits from corporate income tax; an activity where the manager withdraws the entire result does not automatically gain from it.

On rates, a reduced rate of 15% applies to a first bracket of profit, subject to conditions relating to revenue, full payment of capital, and majority ownership by individuals. Beyond this bracket, the standard rate applies. As these thresholds are periodically revised, they must be checked for the relevant financial year.

Deductible expenses: four cumulative conditions

An expense is only deductible if it meets all of the following conditions:

• It is incurred in the interest of the business, and not for the manager's personal benefit.
• It results in a decrease in net assets, which excludes expenditures that actually constitute a capital asset.
• It is recorded in the financial year in which it was incurred.
• It is substantiated by valid supporting documentation.

The fourth condition causes the most lost deductions, and it is purely a matter of documentation. A genuine and perfectly legitimate expense becomes non-deductible for lack of a compliant invoice. This is also the area where the rollout of electronic invoicing is changing practices: the reliable audit trail, which links the invoice to the economic flow and to payment, is becoming the standard of proof. Our article on the reliable audit trail details what this requirement covers.

Certain expenses are excluded by nature, regardless of their usefulness: fines and penalties, lavish expenditures, and part of the costs related to passenger vehicles.

Investments: depreciate, provision, or deduct

Three treatments coexist and are not interchangeable.

Depreciation spreads the deduction of a capital asset over its useful life. The choice of method and duration is not free: it must reflect the actual consumption of the expected economic benefits. The applicable rules are detailed in our article on accounting depreciation.

A provision anticipates a probable and clearly specified expense. Its deductibility requires that the event be ongoing at the closing date and that the amount can be estimated with sufficient accuracy. A flat-rate provision, calculated as a percentage without individual analysis, is regularly rejected — see our rules applicable to provisions.

Immediate deduction remains possible for low-value assets, below a per-unit threshold, as well as for maintenance expenses that do not extend the asset's useful life. The line between deductible maintenance and improvements that must be capitalized is a classic point of tax adjustment.

VAT, a cash-flow issue as much as a tax issue

VAT is not an expense for the liable business, but it weighs on its cash flow and accounts for a significant share of adjustments.

Deducting input VAT requires a compliant invoice showing all mandatory details, an expense incurred for the needs of transactions giving rise to a right of deduction, and the tax becoming chargeable at the supplier's level. Certain expenses are excluded from the right of deduction, notably those relating to passenger vehicles and certain accommodation services.

A VAT credit may be refunded rather than carried forward, which usefully changes the cash-flow profile of businesses in an investment phase. The details are set out in our article on VAT credit adjustment and refund.

Incentive schemes, to be assessed before committing to them

Research tax credit, innovation tax credit, apprenticeship support, exemptions linked to geographic location: these schemes represent significant amounts, but their logic is the same. They require documentation built up continuously, not reconstructed in the year of an audit.

A research tax credit without a technical supporting file and without tracking time spent per project is a fragile tax credit. The amount obtained and the amount retained after an audit are two different things, and the gap depends entirely on the quality of the file.

What an audit looks at

The standard statute-of-limitations period allows the tax authorities to adjust the three preceding financial years. The most frequent points of adjustment are stable from year to year:

• Unsubstantiated or insufficiently substantiated expenses.
• Confusion between personal and business assets, particularly regarding vehicles, travel expenses, and mixed-use premises.
• Insufficiently individualized provisions.
• Capitalizable expenditures recorded as expenses.
• VAT deducted on expenses excluded from the right of deduction.

Rights and obligations during the procedure — response deadlines, guarantees, appeal options — are covered in our article on tax audits.

Use cases

Starting a business. The choice of regime should be made based on a three-year projection of the manager's withdrawals, not solely on the displayed tax rate. This is the decision with the greatest cumulative impact.

Unexpectedly profitable year. The legitimate year-end levers are limited: recognize justified provisions, incur genuinely useful expenses before closing, verify that depreciation has been properly applied. Decisions made after closing have no retroactive effect.

Significant investment. The choice between immediate deduction and depreciation should be prepared before commitment, since it depends on the nature of the asset rather than on a discretionary choice.

Frequently asked questions

Which tax regime should be chosen? It mainly depends on what the manager withdraws. The corporate regime suits businesses that reinvest, since undistributed profit is taxed only at the company level. Taxation at the partner level taxes the entire profit, whether withdrawn or not.

Is a business expense always deductible? No. It must be incurred in the interest of the business, decrease net assets, be recorded in the correct financial year, and be substantiated. Certain categories are excluded by nature, such as fines and lavish expenditures.

Can a vehicle be deducted? Partially. Passenger vehicles are subject to a cap on deductible depreciation and are excluded from the right to deduct VAT. Utility vehicles are subject to a different regime.

Is a provision freely deductible? No. It requires a probable, clearly specified expense, with the event ongoing at closing. A flat-rate provision, calculated without a case-by-case analysis, is regularly challenged.

How many years back can the tax authorities go? The standard statute-of-limitations period covers the three preceding financial years, with extended periods in certain situations, notably in cases of undisclosed activity.

Is the research tax credit risky? The scheme itself is not; a file put together after the fact is. Technical documentation and time tracking per project must be produced on an ongoing basis so that the credit obtained can withstand an audit.

Key takeaways

Three decisions determine a business's actual tax burden, and they are made upfront: the tax regime, decided based on the manager's actual withdrawals rather than the displayed rate; the treatment of investments, between immediate deduction, depreciation, and provisions; and the quality of supporting documentation.

This last point is the least glamorous and the most profitable. Most adjustments do not penalize questionable schemes but genuine expenses that are poorly documented. Bookkeeping in which every entry is linked to valid supporting documentation retains, after an audit, what approximate bookkeeping will only have declared.