fr_bareme_km

SWI-Prolog facts and calculator for the French tax mileage allowance scale ("bareme kilometrique"), used to deduct professional travel costs ("frais reels") from French income tax.

5 tax returns: declaration years 2022 to 2026 (income years 2021 to 2025)
3 vehicle types: automobile, motocyclette (more than 50 cm3), cyclomoteur
135 facts, 3 distance bands per horsepower class
20 % increase for 100 % electric vehicles Online calculator (French): https://macalculatriceenligne.com/finance/divers/calcul-frais-kilometriques/

Installation

?- pack_install(fr_bareme_km).

Usage

?- use_module(library(fr_bareme_km)).

% 2026 scale (2025 kilometres), 5 CV car, 4 000 km
?- frais_km(2026, automobile, 5, 4000, M).
M = 2544.

% Same car, 100 % electric (+20 %)
?- frais_km(2026, automobile, 5, 4000, [electrique(true)], M).
M = 3052.8.

% Raw facts
?- bareme_km(2026, motocyclette, cv_plus_de_5, T, F).
T = tranche(0, 3000),     F = formule(0.606, 0) ;
T = tranche(3000, 6000),  F = formule(0.079, 1583) ;
T = tranche(6000, inf),   F = formule(0.343, 0).

Schema

bareme_km(Annee, Vehicule, Classe, tranche(Min, Max), formule(Coef, Constante))

Argument	Meaning
Annee	Year of the tax return (2022..2026). Kilometres are those of the previous year, see annee_revenus/2.
Vehicule	`automobile`, `motocyclette`, `cyclomoteur`
Classe	automobile: `cv3_et_moins`, `cv4`, `cv5`, `cv6`, `cv7_et_plus`; motocyclette: `cv1_2`, `cv3_4_5`, `cv_plus_de_5`; cyclomoteur: `toutes`
tranche	Band applies when Min < Km =< Max (first band 0 =< Km =< Max), `inf` for the last band
formule	Amount in euros = Km * Coef + Constante

Predicates:

frais_km(+Annee, +Vehicule, +CV, +Km, -Montant): amount in euros, rounded to the cent.
frais_km(+Annee, +Vehicule, +CV, +Km, +Options, -Montant): option electrique(true).
classe_puissance(+Vehicule, +CV, -Classe): maps an integer horsepower to its class.
`annee_revenus(?AnneeDeclaration, ?AnneeRevenus)`.
`source_bareme(?AnneeDeclaration, ?Source)`: official text used for each year.

Electric vehicles

The code applies the 20 % increase to the computed amount, as written in the tax code (CGI, annexe IV, art. 6 B, II). The DGFiP brochure also prints separate electric tables whose coefficients are rounded to three decimals; results can differ from those tables by less than one euro.

Sources and verification

Every value was checked against the official text for its year:

Declaration year	Income year	Official source
2022	2021	BOFIP BOI-BAREME-000001-20230720
2023	2022	BOFIP BOI-BAREME-000001-20230720
2024	2023	DGFiP brochure pratique IR 2024
2025	2024	DGFiP brochure pratique IR 2025
2026	2025	service-public.gouv.fr A14686 and DGFiP brochure pratique IR 2026

The scale was raised by 10 % in 2022 and by 5.4 % in 2023, then kept unchanged for the 2024, 2025 and 2026 tax returns.

Dataset: MaCalculatriceEnLigne, "Bareme kilometrique fiscal France 2022-2026", Mendeley Data, V1, doi:10.17632/5s59m9wycw.1 (CC BY 4.0).

This package is an aid to calculation, not tax advice. The official texts prevail.

Tests

cd test
swipl -g run_tests -t halt test_fr_bareme_km.pl

Licence

Code: MIT (see LICENSE). Data: official French tax data under the Licence Ouverte / Open Licence (Etalab), see LICENSE for attribution.