WLTP is a lab figure measured in mild conditions. In a British winter — cold battery, heater on, motorway speeds — you'll see noticeably less. Enter a WLTP range to get a realistic estimate.
On a cold winter run expect roughly 180 miles from a 257-mile WLTP car — about 30% less than the headline. In mild weather, nearer 218 miles.
These are rules of thumb from owner reports, not a physics model. We take the WLTP figure and apply two multipliers: about 85% in mild weather and about 70% in a cold winter. Your own mileage will vary with speed, terrain, tyres and how you drive — so treat the result as a sensible ballpark.