Forecast

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Senate

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  1. 71%
    Democrats gain control of the Senate in 71% of our simulations.
  2. 22%
    The Senate splits 50-50 in 22% of our simulations. The vice president decides the balance of power in that case.
  3. 7%
    Republicans keep control of the Senate in 7% of our simulations.

We simulated a Nov. 8 election 100 million times using our state-by-state probabilities. In 71.1 million simulations, Democrats ended up with at least 51 seats. Therefore, we say Democrats have a 71.1 percent chance of gaining control of the Senate.

Number of simulated elections (in millions)
Seats controlled by each party
← Democrat majority
Republican majority →
  • 55
    45
  • 54
    46
  • 6.8
    53
    47
  • 26.3
    52
    48
  • 37.0
    51
    49
  • 22.0
    50
    50
  • 6.0
    49
    51
  • 48
    52
  • 47
    53

Both independent senators, Bernie Sanders and Angus King, caucus with the Democratic Party. We count them as Democrats in our calculations.

The 2016 Senate consists of 54 Republicans and 46 Democrats. (The two independent senators caucus with Democrats.) Voters usually re-elect their incumbent senators, but some seats could flip to the other party.

If four Republican Senate seats flip to Democrats and there are no other changes, the 2017 Senate will be split 50-50.

States Likely To Flip

Our algorithm suggests these states have at least a 50 percent chance of flipping.

Click or tap a race to see our calculations

Likely Winner
Democrat
Toss-Up
Republican

  • 99.1% chance Illinois will flip to a Democrat

    1. Tammy Duckworth (D) won against incumbent Mark Kirk (R) in 100.0% of our simulations.
    2. Our simulated populations were 11.0% undecided on average. We penalized the winner's chances by 0.9 percentage points.
    3. Our adjusted probability is 99.1% Democrat.
    Percentage
    Point Lead
    D+20
    D+10
    0
    R+10
    R+20
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    D+11.9
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 98.2% chance Wisconsin will flip to a Democrat

    1. Russell Feingold (D) won against incumbent Ronald Johnson (R) in 99.9% of our simulations.
    2. Our simulated populations were 6.9% undecided on average. We penalized the winner's chances by 1.6 percentage points.
    3. Our adjusted probability is 98.2% Democrat.
    Percentage
    Point Lead
    D+16
    D+8
    0
    R+8
    R+16
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    D+4.2
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 97.8% chance Pennsylvania will flip to a Democrat

    1. Kathleen McGinty (D) won against incumbent Patrick Toomey (R) in 99.9% of our simulations.
    2. Our simulated populations were 7.0% undecided on average. We penalized the winner's chances by 2.1 percentage points.
    3. Our adjusted probability is 97.8% Democrat.
    Percentage
    Point Lead
    D+8
    D+4
    0
    R+4
    R+8
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    D+3.4
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 86.7% chance Indiana will flip to a Democrat

    1. Evan Bayh (D) won against Todd Young (R) in 90.9% of our simulations.
    2. Our simulated populations were 9.3% undecided on average. We penalized the winner's chances by 4.2 percentage points.
    3. Our adjusted probability is 86.7% Democrat.
    Percentage
    Point Lead
    D+20
    D+10
    0
    R+10
    R+20
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    D+2.2
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 83.1% chance New Hampshire will flip to a Democrat

    1. Maggie Hassan (D) won against incumbent Kelly Ayotte (R) in 87.0% of our simulations.
    2. Our simulated populations were 4.6% undecided on average. We penalized the winner's chances by 3.9 percentage points.
    3. Our adjusted probability is 83.1% Democrat.
    Percentage
    Point Lead
    D+8
    D+4
    0
    R+4
    R+8
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    D+1.2
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • Toss-up in Missouri

    1. Incumbent Roy Blunt (R) won against Jason Kander (D) in 54.5% of our simulations.
    2. Our simulated populations were 7.9% undecided on average. We penalized the winner's chances by 4.5 percentage points.
    3. That left us with a toss-up.
    Percentage
    Point Lead
    D+16
    D+8
    0
    R+8
    R+16
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    R+0.1
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

States Less Likely To Flip

Our algorithm suggests these states have less than a 50 percent chance of flipping.

Likely Winner
Democrat
Toss-Up
Republican

  • 100.0% chance California will remain with a Democrat

    1. In California, Democrat Kamala Harris is competing against Democrat Loretta Sanchez.
    2. Therefore, the probability of a Democrat winning is 100.0%.

  • 99.8% chance New York will remain with a Democrat

    1. Incumbent Charles Schumer (D) won against Wendy Long (R) in 100.0% of our simulations.
    2. Our simulated populations were 8.4% undecided on average. We penalized the winner's chances by 0.2 percentage points.
    3. Our adjusted probability is 99.8% Democrat.
    Percentage
    Point Lead
    D+50
    D+25
    0
    R+25
    R+50
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    D+40.6
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 99.7% chance Maryland will remain with a Democrat

    1. Christopher Van Hollen (D) won against Kathy Szeliga (R) in 100.0% of our simulations.
    2. Our simulated populations were 9.7% undecided on average. We penalized the winner's chances by 0.3 percentage points.
    3. Our adjusted probability is 99.7% Democrat.
    Percentage
    Point Lead
    D+40
    D+20
    0
    R+20
    R+40
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    D+31.3
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 99.3% chance Colorado will remain with a Democrat

    1. Incumbent Michael Bennet (D) won against Darryl Glenn (R) in 100.0% of our simulations.
    2. Our simulated populations were 6.7% undecided on average. We penalized the winner's chances by 0.7 percentage points.
    3. Our adjusted probability is 99.3% Democrat.
    Percentage
    Point Lead
    D+20
    D+10
    0
    R+10
    R+20
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    D+9.6
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 98.8% chance Connecticut will remain with a Democrat

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Connecticut Senate race is: solidly Democrat.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance Hawaii will remain with a Democrat

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Hawaii Senate race is: solidly Democrat.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance Oregon will remain with a Democrat

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Oregon Senate race is: solidly Democrat.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance Vermont will remain with a Democrat

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Vermont Senate race is: solidly Democrat.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance Washington will remain with a Democrat

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Washington Senate race is: solidly Democrat.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 65.2% chance Nevada will remain with a Democrat

    1. Catherine Cortez-Masto (D) won against Joe Heck (R) in 75.2% of our simulations.
    2. Our simulated populations were 8.6% undecided on average. We penalized the winner's chances by 10.0 percentage points.
    3. Our adjusted probability is 65.2% Democrat.
    Percentage
    Point Lead
    D+8
    D+4
    0
    R+4
    R+8
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    D+0.8
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 88.0% chance North Carolina will remain with a Republican

    1. Incumbent Richard Burr (R) won against Deborah Ross (D) in 92.1% of our simulations.
    2. Our simulated populations were 6.6% undecided on average. We penalized the winner's chances by 4.1 percentage points.
    3. Our adjusted probability is 88.0% Republican.
    Percentage
    Point Lead
    D+10
    D+5
    0
    R+5
    R+10
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    R+1.6
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 93.3% chance Alaska will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Alaska Senate race is: likely Republican.
    3. Since 2004, Cook has been right about this call in 93.3% of all Senate races.

  • 98.7% chance Florida will remain with a Republican

    1. Incumbent Marco Rubio (R) won against Patrick Murphy (D) in 100.0% of our simulations.
    2. Our simulated populations were 6.3% undecided on average. We penalized the winner's chances by 1.3 percentage points.
    3. Our adjusted probability is 98.7% Republican.
    Percentage
    Point Lead
    D+10
    D+5
    0
    R+5
    R+10
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    R+5.0
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 98.8% chance Alabama will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Alabama Senate race is: solidly Republican.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance Arkansas will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Arkansas Senate race is: solidly Republican.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance Idaho will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Idaho Senate race is: solidly Republican.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance Kentucky will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Kentucky Senate race is: solidly Republican.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance Louisiana will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Louisiana Senate race is: solidly Republican.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance North Dakota will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the North Dakota Senate race is: solidly Republican.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance Oklahoma will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the Oklahoma Senate race is: solidly Republican.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance South Carolina will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the South Carolina Senate race is: solidly Republican.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 98.8% chance South Dakota will remain with a Republican

    1. Since we haven't collected enough polls for this state, we rely on Cook Political Report's Senate Ratings.
    2. The Cook rating for the South Dakota Senate race is: solidly Republican.
    3. Since 2004, Cook has been right about this call in 98.8% of all Senate races.

  • 99.4% chance Georgia will remain with a Republican

    1. Incumbent John Isakson (R) won against James Barksdale (D) in 100.0% of our simulations.
    2. Our simulated populations were 5.8% undecided on average. We penalized the winner's chances by 0.6 percentage points.
    3. Our adjusted probability is 99.4% Republican.
    Percentage
    Point Lead
    D+20
    D+10
    0
    R+10
    R+20
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    R+10.1
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 99.5% chance Iowa will remain with a Republican

    1. Incumbent Charles Grassley (R) won against Patty Judge (D) in 100.0% of our simulations.
    2. Our simulated populations were 7.8% undecided on average. We penalized the winner's chances by 0.5 percentage points.
    3. Our adjusted probability is 99.5% Republican.
    Percentage
    Point Lead
    D+30
    D+15
    0
    R+15
    R+30
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    R+16.2
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 99.5% chance Ohio will remain with a Republican

    1. Incumbent Robert Portman (R) won against Ted Strickland (D) in 100.0% of our simulations.
    2. Our simulated populations were 7.3% undecided on average. We penalized the winner's chances by 0.5 percentage points.
    3. Our adjusted probability is 99.5% Republican.
    Percentage
    Point Lead
    D+30
    D+15
    0
    R+15
    R+30
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    R+16.1
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 99.6% chance Arizona will remain with a Republican

    1. Incumbent John McCain (R) won against Ann Kirkpatrick (D) in 100.0% of our simulations.
    2. Our simulated populations were 4.0% undecided on average. We penalized the winner's chances by 0.4 percentage points.
    3. Our adjusted probability is 99.6% Republican.
    Percentage
    Point Lead
    D+16
    D+8
    0
    R+8
    R+16
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    R+9.5
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 99.8% chance Kansas will remain with a Republican

    1. Incumbent Jerry Moran (R) won against Patrick Wiesner (D) in 100.0% of our simulations.
    2. Our simulated populations were 7.0% undecided on average. We penalized the winner's chances by 0.2 percentage points.
    3. Our adjusted probability is 99.8% Republican.
    Percentage
    Point Lead
    D+40
    D+20
    0
    R+20
    R+40
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    R+32.9
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

  • 99.8% chance Utah will remain with a Republican

    1. Incumbent Mike Lee (R) won against Misty Snow (D) in 100.0% of our simulations.
    2. Our simulated populations were 6.9% undecided on average. We penalized the winner's chances by 0.2 percentage points.
    3. Our adjusted probability is 99.8% Republican.
    Percentage
    Point Lead
    D+40
    D+20
    0
    R+20
    R+40
    July 1
    Nov. 8
    Election Day
    Loading…
    Latest Average
    R+33.2
    Our algorithm simulates 5,000 random populations whose voting intentions correspond to poll results. For illustration, we plot 200 of these populations and show the average.
    Poll data from HuffPost Pollster

We calculate the probable outcome for each individual Senate race, and then we use those probabilities to determine the likely seat counts on election night.

1. State-By-State Probabilities

We estimate the probability of a win in each Senate race using publicly available polls in the HuffPost Pollster database. We use Pollster’s Bayesian Kalman filter model to simulate 100,000 populations whose voting intentions correspond to the poll results. (We sample 5,000 of those simulations in our calculations, for speed.)

When there are fewer than five available polls in 2016 or fewer than two polls since July 2016, we use Cook Political Report ratings to estimate where the race stands.

We run the simulations out to Election Day, Nov. 8. Since we don’t have polling data for the future, the model assumes voter intentions generally continue along their current trajectories. Projections will become more certain as more polls are published.

The model also estimates what proportion of voters is undecided according to the polls as of today. We penalize the leader’s win probability based on this formula: percent undecided ÷ (leader’s poll average − runner-up’s poll average) × 100 percent. The smaller the margin between candidates, the greater the chance that undecided voters will affect the outcome. We subtract that number from the overall probability of a candidate winning.

Download our state-by-state probabilities TSV file.

2. Likely Seat Counts

Finally, we simulate a Nov. 8 election 100 million times using the state-by-state probabilities. The proportion of times Democrats end up with at least 51 seats is the probability of the Democrats gaining control of the Senate. The probability of a tie is the proportion of times the seat count lands at 50-50.

Download our likely seat counts TSV file.

Find out more about our methodology.