French BTP Price Revision Calculator
Initial price, fixed portion, and one or several weighted INSEE BT/TP indices: calculate the revised price on a French works contract using the standard parametric formula Pn = P0 × (a + b × In/I0), or its multi-index variant.
Usually between 10% and 15% depending on the contract, 12.5% shown as an indicative default, replace it with your contract's own value.
Find published index values on insee.fr (French), using the index your contract specifies (BT01, BT06, TP01...).
This calculation comes back with every progress statement. Mirage prepares it.
Mirage builds your monthly progress statement (situation de travaux) from the DPGF and site progress, every line traced to its source. Send us a past statement and we send back a plan, no commitment.
See automated progress statements (in French)
Prefer to talk it through? Book a call
Frequently asked questions
Pn = P0 × (a + b × In/I0), where P0 is the initial price, a is the fixed (non-revisable) portion, b is the variable portion (a + b = 1), and In/I0 is the ratio between the index for the month the work was carried out (or the month your revision clause names) and the index for the contract's reference month (month zero). Some contracts weight several indices instead of one: Pn = P0 × (a + b1 × I1n/I1_0 + b2 × I2n/I2_0 + ...), this calculator supports both.
INSEE (France's national statistics office) publishes several BT (Bâtiment) and TP (Travaux Publics) indices by trade: BT01 (all trades), BT02 (earthworks), BT03 (masonry and concrete pipes), BT06 (reinforced concrete structure), BT18a (interior woodwork), BT38 (plumbing), BT47 (electrical), etc. The contract should specify which one applies, if it doesn't, the index closest to the actual trade is used.
The contract's specific administrative clauses (CCAP) set it explicitly, usually between 0.10 and 0.15. This calculator defaults to 0.125 as an indicative midpoint, not a legally mandated value, always check your own contract's revision clause.
Some contracts cap how far the revision coefficient can move in either direction, e.g. never below 0.95 or above 1.05, to limit exposure on both sides. It isn't automatic: it only applies if your contract's revision clause explicitly sets one. This calculator lets you enter one optionally.
Yes, but only if the private contract explicitly includes a price revision clause, common on longer projects, but never automatic the way it is on a French public contract governed by the Code de la commande publique.
Price revision only corrects a number that was right to begin with. Mirage helps construction companies bidding on French projects make the takeoff and price schedule behind that number reliable in the first place.
See Construction Intelligence