Calculation method and sources

Three datasets drive the site: the Tempo colours published by RTE, the regulated tariff grid and national electricity demand. Each is read by a replayable script in the repository, dated, and used by every page: no price and no colour is typed by hand into a text.

The colour of the day: read from RTE several times a day

The colour comes from the open data behind RTE’s “Tempo calendar” page, which states that the binding colour is the one published at 10:30 the day before. The script scripts/data/fetch-tempo.mjs rereads the current season and tomorrow’s colour, checks the quotas (22 red, 43 white) and the placement rules (no red at weekends or outside 1 November to 31 March, no white on Sundays), then writes the colour file. A scheduled job rebuilds and republishes the site every day, just after 10:30 and again around midnight. If RTE does not answer, the previous reading is kept and its date stays on screen. Last reading: , 13 seasons on file, from 2014-2015 to 2026-2027.

In the browser, the “today” card follows Paris time: after midnight it moves to the new date without waiting for the next rebuild, and reminds you that before 06:00 the current Tempo day is still the previous one.

Prices: the blue tariff grid of 1 August 2026

Standing charges and kWh prices, all taxes included, are those of the official “Tarif Bleu” grid applicable from 1 August 2026, set on the energy regulator’s proposal (CRE deliberation no. 2026-147 of 15 July 2026). Base: €0.2001 per kWh at 3 and 6 kVA, €0.1985 above, with 9 to 36 kVA closed to new contracts. Off-peak: €0.2142 and €0.1589, available from 3 kVA. Tempo, from 6 kVA: from €0.1356 (blue off-peak) to €0.7295 (red peak). The next change is expected on 1 February 2027, with a further cut in the excise duty announced by the regulator (article 71 of the 2026 finance act); the grid was not yet published on 16 October 2026; the grid will be reread and the parameter file updated the day it is published.

How much of your use lands on a red day

That question decides Tempo, and most calculators answer it in proportion to the number of days. We take it from grid measurements. The script scripts/data/build-profil.mjs reads national demand day by day (éCO2mix, RTE final data), takes the summer baseline off each day (median of May to September) and keeps the part that depends on the cold. Over 12 completed seasons, that heating part falls 19.4 % on red days, 29.4 % on white days and 51.2 % on blue days. Each day is cut like a Tempo day, from 06:00 to 06:00 the next morning, Paris time, from the quarter-hour readings: the night after a red day counts with it, as on the bill. Until 16 October 2026 the calendar day was used as an approximation; the exact cut moves the red-day share from 19.2% to 19.4%.

The comparison formulas

  • Heating h = 1 − 12 × (summer month) ÷ (annual use), bounded between 0 and 1.
  • Share of a colour c: (1 − h) × days(c) ÷ 365 + h × profile(c), with 300, 43 and 22 days.
  • Tempo cost: for each colour, kWh × [n × off-peak price + (1 − n) × peak price], n being the off-peak share; on a red day the shifted share e moves e × (1 − n) of peak use to off-peak.
  • Off-peak option cost: kWh × [n × €0.1589 + (1 − n) × €0.2142]; Base: kWh × the price for the power.
  • Each option adds twelve times its monthly standing charge at the chosen power.

Example checked by the tests: 8,000 kWh at 6 kVA, no heating, 35% off-peak. Base €1,791.12, Off-peak €1,749.08, Tempo €1,632.83 a year.

Tests that block publication

  • Grid prices and standing charges, option by option, and no Tempo at 3 kVA.
  • Five bills recalculated by hand (Base, Off-peak, Tempo with and without shifting, Base 9 kVA), to the cent.
  • Every completed season: 22 red and 43 white days (18 and 47 in 2019-2020), no red at a weekend, on a holiday or out of period, no white on a Sunday, at most 5 red days running.
  • The current season: days left plus days published equal the quotas, and enough weekdays remain to place the red days still to come.
  • Every mini-calculator, in both languages, with no missing value.

What the site does not do

  • It does not forecast colours beyond what RTE has published: no “9-day forecast”.
  • It does not know your exact off-peak hours, only the share you enter; the real windows are set by Enedis for your meter.
  • It calculates the regulated tariff, not market offers. The grid’s standing charge surcharges (no Linky meter, no reading sent for twelve months, self-generation feeding the grid) can be chosen in the comparison; they are added, with 20% VAT, in the same way to all three options and so do not change the ranking.
  • It does not cover Corsica or the overseas territories, whose off-peak and Tempo rules differ.

Updates

Colours: every day. Prices: at each regulated tariff change, usually in February and August. Heating profile: once a year, after the season closes on 31 August. An error reported to contact@tempodemain.fr is checked against the source, corrected and turned into a test. See the editorial policy.

All sources

Parameters read on · page rebuilt on · last review .

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Publisher of household electricity calculators · Tempo option, off-peak hours, regulated tariff

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Regulated tariff 2026, checked on