On 21 July, Joe Biden dropped out of the presidential race and endorsed Kamala Harris. This historic move changed the landscape of the election and how many felt about the race. As the election enters its final weeks, Guardian US is averaging national and state polls to see how the two candidates are faring. We will update our averages once a week, or more if there is major news.

Latest analysis: Harris’s national poll lead is increasing. Even by small margins, these increases may turn out to be significant. Poll-watchers are saying that Harris might not need as big a popular vote lead as Democrats have needed in the past. The reason, roughly summarised, is that while Harris is sustaining narrow leads in Pennsylvania, Michigan and Wisconsin, Trump is polling better than four years ago in states he still has little chance of winning. An improvement in a non-competitive state is an improvement that will not help him win.

With just over five weeks to go before polling day, none of this is predictive of a final outcome. But it may suggest a scenario where the candidate destined for the White House is the one who wins the most votes – which, after all, is how democracy is meant to work. – Robert Tait, 28 September

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Notes on data

To calculate our polling averages, Guardian US took a combination of head-to-head and multi-candidate polls and calculated a rolling 10-day average for each candidate. Our tracker uses polls gathered by 538 and filters out lower-quality pollsters for national polls. Our state polling averages use a lower quality threshold for inclusion due to the small numbers of state polls. If there were no polls over the the 10-day period, we leave the average blank.

Polling averages capture how the race stands at a particular moment in time and are likely to change as the election gets closer. Averages from states with small numbers of polls are also more susceptible to errors and biases. Our averages are an estimate of the support that the candidates have in key swing states and on the national stage. The election is decided by the electoral college, so these averages should not be taken as a likelihood of winning the election in November.

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