Live forecast methodology

As individual constituency results are declared on election night, it is not always clear how the election is playing out nationwide. We expect comfortable Labour victories in the first seats to declare, in the north-east of England, for example, but these may not be representative of the country as a whole. To track how many seats we expect each party to win, we simulate the election in each constituency based on pre-election forecasts, the exit poll, and results as they are declared.

The starting point for our live model is our pre-election forecast. Once the exit poll is released, at 10pm, we incorporate the seat estimates into our model—narrowing the range of possible outcomes. As results come in, we update the model to include the trends seen in the new data. If a party is under- or over-performing expectations, or performing particularly well in certain areas, we extrapolate that across the remaining constituencies. We run 10,000 simulations to give a range of possible outcomes across the country.