Republicans keep control of the Senate in 7% of our simulations.

The Senate splits 50-50 in 22% of our simulations. The vice president decides the balance of power in that case.

Democrats gain control of the Senate in 71% 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.

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 IL Illinois Currently Republican 99.1% chance Illinois will flip to a Democrat Tammy Duckworth (D) won against incumbent Mark Kirk (R) in 100.0% of our simulations. Our simulated populations were 11.0% undecided on average. We penalized the winner's chances by 0.9 percentage points. Our adjusted probability is 99.1% Democrat. Percentage

Point Lead D+20 D+10 0 R+10 R+20 Election Day Loading… Latest Average 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

WI Wisconsin 98.2% chance Wisconsin will flip to a Democrat Russell Feingold (D) won against incumbent Ronald Johnson (R) in 99.9% of our simulations. Our simulated populations were 6.9% undecided on average. We penalized the winner's chances by 1.6 percentage points. Our adjusted probability is 98.2% Democrat. Percentage

Point Lead D+16 D+8 0 R+8 R+16 Election Day Loading… Latest Average 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

PA Pennsylvania 97.8% chance Pennsylvania will flip to a Democrat Kathleen McGinty (D) won against incumbent Patrick Toomey (R) in 99.9% of our simulations. Our simulated populations were 7.0% undecided on average. We penalized the winner's chances by 2.1 percentage points. Our adjusted probability is 97.8% Democrat. Percentage

Point Lead D+8 D+4 0 R+4 R+8 Election Day Loading… Latest Average 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

IN Indiana 86.7% chance Indiana will flip to a Democrat Evan Bayh (D) won against Todd Young (R) in 90.9% of our simulations. Our simulated populations were 9.3% undecided on average. We penalized the winner's chances by 4.2 percentage points. Our adjusted probability is 86.7% Democrat. Percentage

Point Lead D+20 D+10 0 R+10 R+20 Election Day Loading… Latest Average 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

NH New Hampshire 83.1% chance New Hampshire will flip to a Democrat Maggie Hassan (D) won against incumbent Kelly Ayotte (R) in 87.0% of our simulations. Our simulated populations were 4.6% undecided on average. We penalized the winner's chances by 3.9 percentage points. Our adjusted probability is 83.1% Democrat. Percentage

Point Lead D+8 D+4 0 R+4 R+8 Election Day Loading… Latest Average 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

MO Missouri Toss-up in Missouri Incumbent Roy Blunt (R) won against Jason Kander (D) in 54.5% of our simulations. Our simulated populations were 7.9% undecided on average. We penalized the winner's chances by 4.5 percentage points. That left us with a toss-up. Percentage

Point Lead D+16 D+8 0 R+8 R+16 Election Day Loading… Latest Average 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.