1. The short answer
Winter diesel is diesel with a lowered Cold Filter Plugging Point (CFPP) so paraffin wax dissolved in the fuel does not crystallise and block the fuel filter in cold weather, and the CFPP limit, along with the calendar date it starts, differs by country. Diesel naturally contains paraffins; as temperature falls, these first form microscopic crystals that make the fuel look hazy, the cloud point, and then, at a slightly lower temperature, the crystals grow enough to clog the fine mesh of a fuel filter, the exact point a CFPP test measures. A vehicle can pass its cloud point and keep running for a while, then still fail once it reaches its CFPP.
EN 590, the European diesel standard, sets CFPP classes from A (+5C) down to F (-20C) for temperate climates, and 0 (-20C) down to 4 (-44C) for arctic climates (Wikipedia, EN 590, accessed 18 September 2026). Which class is actually sold, and when the switch happens, is set nationally, not by EN 590 itself.
2. Who sets the switch, and why it strains supply this autumn
Refiners and blenders lower the CFPP by adjusting the crude mix and adding cold-flow additives, or, in the United States, by blending in lighter No. 1 kerosene, and every one of those changes uses refinery capacity that would otherwise go toward ordinary diesel output. Producing winter grade is not a label change, it changes what leaves the distillation column, and the changeover follows a fixed calendar in Europe or a statistical cold-snap threshold in the United States, never demand.
That timing matters more this year because the changeover lands on top of an already tight market. How constrained refinery throughput already is, is tracked on our refinery utilisation entry. The extra blending capacity that winter grade requires competes directly with the volumes described on our diesel shortage entry, where distillate stocks are already running below their five-year average. In a normal year the switch is routine; in a year with stocks already stretched, it is one more claim on the same barrels.
3. Grades and switch dates by country
The table below lists only dates confirmed in a dated national source. For France and Spain, this research found no confirmed national switch date, and we say that plainly here rather than guessing one.
| Country | Grade | CFPP / cloud point | Period | Source | As of |
|---|---|---|---|---|---|
| Germany | Summer diesel | CFPP 0C | 15 Apr to 30 Sep | Wikipedia, Winterdiesel | accessed 18 Sep 2026 |
| Germany | Transitional | CFPP -10C | 1 Oct to 15 Nov and 1 Mar to 14 Apr | Wikipedia; confirmed by Promobil | 18 Sep 2026 / 15 Nov 2025 |
| Germany | Winter diesel | CFPP -20C | 16 Nov to 28 Feb | Wikipedia; confirmed by Promobil | 18 Sep 2026 / 15 Nov 2025 |
| Austria | Summer diesel | CFPP +5C | 1 Apr to 30 Sep | Wikipedia, Winterdiesel | accessed 18 Sep 2026 |
| Austria | Transitional | CFPP +5C to -20C | 1 Oct to 31 Oct | Wikipedia, Winterdiesel | accessed 18 Sep 2026 |
| Austria | Winter diesel | CFPP -20C | 1 Nov to 28 Feb | Wikipedia, Winterdiesel | accessed 18 Sep 2026 |
| Austria | Transitional | CFPP -15C | 1 Mar to 31 Mar | Wikipedia, Winterdiesel | accessed 18 Sep 2026 |
| Switzerland | Year-round | CFPP -20C | no seasonal switch | Wikipedia, Winterdiesel | accessed 18 Sep 2026 |
| United Kingdom | Summer | CFPP max -5C, typ. -8C | 16 Mar to 21 Oct | Crown Oil | accessed 18 Sep 2026 |
| United Kingdom | Winter | CFPP max -15C, typ. -20C | 22 Oct to 15 Mar | Crown Oil | accessed 18 Sep 2026 |
| United States | No fixed date | Cloud point at most 6C above 10th-percentile minimum | set monthly per state, ASTM D975 | Wikipedia, Winter diesel fuel | accessed 18 Sep 2026 |
| France | No confirmed date | no confirmed CFPP threshold found | Arrete sets a framework, no dated threshold verified | Legifrance | accessed 18 Sep 2026 |
| Spain | No confirmed date | not found | not found | not found | not found |
4. Why the numbers you see quoted often disagree
Two very different regulatory philosophies sit behind these figures, which is why a single "winter diesel starts on X date" headline rarely applies everywhere. Europe, under EN 590, assigns fixed CFPP classes to fixed calendar windows that vary by country, while the United States, under ASTM D975, sets no calendar date at all: it requires a cloud point tied to each state's own 10th-percentile minimum temperature for the month, calculated regionally rather than fixed nationally (Wikipedia, Winter diesel fuel, accessed 18 September 2026).
Switching grade is a separate question from the sulphur content of the fuel, covered on our low-sulphur heating oil entry: a winter-grade and a summer-grade diesel can carry the same ultra-low sulphur specification, and cold-flow performance says nothing about the refining margin, which our diesel crack spread entry covers separately.
5. What to check before the first frost
Before the first hard frost, check three concrete things rather than panic-buying: what grade your supplier says is currently going into the tank, your vehicle's or boiler's actual operating temperature range, and your current delivery lead time. Commuters with older diesel vehicles, especially ones parked outdoors or in an unheated garage, are the most exposed once temperatures fall below the CFPP of the fuel already in the tank; a call to your usual filling station about which grade is currently sold costs nothing and settles the question faster than a forum post.
Farmers and hauliers running large outdoor tanks face a second risk: bulk fuel delivered before the switch date can still be sitting in a tank once temperatures drop, regardless of what grade is now sold at the pump, so ask your supplier when your specific delivery was blended, not just what is being sold today. Businesses with fixed delivery schedules should get written confirmation of which CFPP grade the next delivery will meet, especially where tight refinery capacity, described on our heating oil buy now or wait entry, is already slowing lead times.
None of this is a reason to overfill a tank or hoard fuel; it is a reason to ask specific, dated questions of whoever supplies your fuel. To see what a change in diesel or heating oil cost would add to your own bill this winter, our calculator works from your own numbers, not a forecast.
See what a change in diesel or heating oil cost would add to your own bill.
Run the calculator6. What winter diesel is not, and what people get wrong
Winter diesel is not a fuel additive you buy separately, and it is not the same fuel with a marketing sticker: it is diesel a refiner or blender has already reformulated before it reaches the pump. A common mix-up is treating cloud point and CFPP as the same number: cloud point is the higher temperature at which wax first becomes visible, CFPP is the lower, stricter test of when it actually blocks a filter, and casual reporting often conflates the two.
We do not give instructions here for mixing your own cold-flow additive or blending petrol or kerosene into diesel yourself, and we expressly advise against doing this. Additive treatment and any blending of fuels should only be carried out by a qualified supplier or under your vehicle or boiler manufacturer's own approval, because the wrong ratio can damage fuel systems, void a warranty, or, in a heating appliance, create a safety hazard; rules on this vary by country and sometimes by municipality, so check with your supplier, manufacturer or local authority rather than mixing anything yourself. For how long fuel already sitting in your tank stays usable, see our heating oil shelf life entry.