Straight-line and declining-balance depreciation

Sources and assumptions

• bofip.impots.gouv.fr — BOI-BIC-AMT-20-20-30 — tax year 2026, verified on September 4, 2026

  Excerpt from the source : « Aux termes du 1 de l'article 39 A du CGI, les taux d'amortissement dégressif sont obtenus en multipliant les taux d'amortissement linéaire par un coefficient fixé à : - 1,25 lorsque la durée normale d'utilisation est de trois ou quatre ans ; »

• bofip.impots.gouv.fr — BOI-BIC-AMT-20-20-30 — tax year 2026, verified on September 4, 2026

  Excerpt from the source : « les taux d'amortissement dégressif sont obtenus en multipliant les taux d'amortissement linéaire par un coefficient fixé à : [...] - 1,75 lorsque cette durée normale est de cinq ou six ans ; »

• bofip.impots.gouv.fr — BOI-BIC-AMT-20-20-30 — tax year 2026, verified on September 4, 2026

  Excerpt from the source : « les taux d'amortissement dégressif sont obtenus en multipliant les taux d'amortissement linéaire par un coefficient fixé à : [...] - 2,25 lorsque cette durée normale est supérieure à six ans. »

Calculation assumptions

• Twelve-month financial year: the first-year pro rata runs from the month the asset enters service to year end, and the acquisition year counts as a full year when counting the remaining years of the declining-balance schedule.
• For straight-line depreciation, French tax doctrine counts the first-year pro rata in days from the date the asset enters service; this calculator rounds it to whole months, as the declining-balance method does, which runs from the first day of the acquisition month. The gap is at most one month of charge, caught up on the last line.
• Under the declining-balance method, switching to the straight-line charge (net book value ÷ remaining years) is an option open to the business: the calculator applies it as soon as that charge exceeds the declining charge, which is standard practice.
• The residual value you enter is deducted from the depreciable base in both methods: that is the accounting logic. For tax purposes the declining-balance method applies to the full cost — leave 0 to get the tax computation.
• Not modelled: exceptional depreciation, the increased or reduced declining coefficients specific to certain assets, the minimum mandatory depreciation, the component approach, nor the asset's eligibility for the declining method (recalled as a warning, not checked).
• Each annual charge is rounded to the cent and the last line of each schedule is the exact balance: the charges always add up to the depreciable base. The worked examples in the tax doctrine are rounded to the euro.