House 2026

Background

The equation used to predict the Democratic share of the two-party House vote for 2026 is equation 3a in Table 2 in
Presidential and Congressional Vote-Share Equations: November 2022 Update.
The following discussion assumes that the paper,
Presidential and Congressional Vote-Share Equations, American Journal of Political Science, January 2009, 55-72
has been read. You can compute your own vote prediction using your own assumptions about the economy by clicking:
Compute your own prediction for 2026.

Economic Assumptions and Vote Prediction: December 23, 2025

The two economic variables in the equation, using the notation in Table 1 in the above November 2022 update, are

Pcc = the growth rate of the GDP deflator in the first 7 quarters of the second Trump administration, 2025:1-2026:3, at an annual rate,

and

Zcc = 15/7 times the number of quarters in the first 7 quarters of the second Trump administration in which the growth rate of real per capita GDP is greater than 3.2 percent at an annual rate.

As of this writing data are available for the first three quarters of the second Trump administration. For these three quarters the growth rate of the GDP deflator is 3.29 percent at an annual rate and there are 2 strong growth quarters, 2025.2 and 2025.3.

Forecasts of the U.S. economy for 2025.4--2029.4 using the US model are on this website--Economic Forecasts. There is one more strong growth quarter forecast, 2025.4, and inflation is predicted to moderate. Using the actual values for 2025.1--2025.3 and the forecast values for 2025.4--2026.3, the value of Pcc is 2.45 and the value of Zcc is 6.429.

The prediction also needs the values of the two-party Democratic vote share in the 2024 election for the president, Vp-2, and for the House, Vc-2. The value of the former is 49.25 percent (Harris), and the value of the latter is 48.68 (House Democrats).

The following gives a breakdown of the prediction using the notation in Table 1 and the coefficient estimates in equation 3a in Table 2 of the update.

49.04    Constant term
 3.36    Coefficient estimate of I times -1 (the Republican party in power in
         the White House).
-0.92     0.695*(Vc-2 - 50) =  0.695*(48.68 - 50).  House incumbency effect.
 0.17    -0.228*(Vp-2 - 50) = -0.228*(49.25 - 50).  Estimated effect from the
          size of the presidential vote share in the last election 
          (balance effect). 

51.65   TOTAL so far

 0.91    -0.370*Pcc*I.  Assuming Pcc = 2.45.  Inflation effect.
-3.39     0.528*Zcc*I.  Assuming 3 strong growth quarters, 
          where Zcc = (15/7)*3 = 6.429.

49.16   PREDICTED VOTE SHARE FOR DEMOCRATS

The predicted two-party vote share for the House Democrats is 49.16 percent. This is predicted vote share, not seats.

The prediction shows that the Democrats lose more from output growth than they gain from inflation (-3.39 versus 0.91). The Republicans benefit from the fact that the second are third quarters of 2025 are strong growth quarters and that the fourth quarter of 2025 is also forecast to be a strong growth quarter. Also, inflation is forecast to be fairly modest, which doesn't hurt the Repubicans much.

The Democrats are hurt somewhat by the House incumbency effect (-0.92). They are helped slightly by the balance effect, but only slightly (0.17). The main positive effect for the Democrats is the estimated 3.36 gain from the fact that the Republicans are the party in power in the White House. The estimated constant term is slightly in the Republican's favor (49.04).

This prediction will change in the next four quarters as more is known about the economy. You can compute your own vote prediction using your own assumptions about the economy by clicking the above link. If inflation in the next four quarters is larger than the US model forecasts, this will help the Democrats.