Commonwealth Index

The poll average has Democrats at 46.0% and Republicans at 38.6%, with 15.4% undecided or choosing someone else.

Set the undecideds aside, and 84.6% of voters remain. Split that 84.6% between the parties:

Democrats

46.0 ÷ 84.6 = 54.4%

Republicans

38.6 ÷ 84.6 = 45.6%

Margin

54.4 − 45.6 = D+8.8

Elections have no undecided option, so the forecasts use this two-party margin. That assumes undecided voters split the way decided voters already have. The generic ballot chart’s margin is smaller because it keeps undecided voters in the count. Figures are rounded to one decimal, so the result can differ from the slider by a tenth.