For months, we’ve been tracking the probability of each party controlling the Senate after the 2014 elections. Here’s how the chances have changed over time.

Democrats’ chance Republicans’ chance

To forecast each party’s chance of gaining a majority, our model first calculates win probabilities for each individual Senate race. In addition to the latest polls, it incorporates the candidates’ political experience, fund-raising, a state’s past election results and national polling. More about our methodology.

What are the odds of “overtime” — that Senate control hinges on a December runoff in Louisiana? Or that the elections leave Republicans in control of 54 seats or more? In addition to which party controls the Senate, here are some other interesting outcomes worth following.

Probability that... Republicans hold every currently Republican seat 59% Georgia goes to a runoff election in January 48% Republicans control 54 seats or more 24% At least one race we rate as Likely or Solid is won by the underdog 21% Greg Orman wins and caucuses with Democrats* 20% The Senate is split 50-50 13% Control is decided by Greg Orman 9% Control is decided by Louisiana runoff in December 9% Every race is won by the current favorite 5% Democrats control 53 seats or more 2% * Mr. Orman has said he will caucus with the majority party.

With the state-by-state probabilities in hand, our machine randomly simulates all 36 Senate elections. Give it a try below. The spinners are calibrated to the current probabilities we’ve calculated for each state. We let the states move together to some extent, but you’ll no doubt occasionally see some surprising results — over 20 percent of the time, at least one of the races we call “likely” will be won by the opposite party.

We run the above simulation 250,000 times and tally the results. (Don’t worry, we don’t do it by hand.) The table below shows the outcomes of those simulations. By counting up the simulations that resulted in a Republican majority, we can estimate the probability that they will win a majority in the Senate. Likewise for the Democrats.

Dem. Seats Rep. Seats Majority Likelihood 43 57 + 14 Rep. <1% 44 56 + 12 Rep. 1% 45 55 + 10 Rep. 7% 46 54 + 8 Rep. 16% 47 53 + 6 Rep. 22% Likeliest 48 52 + 4 Rep. 22% 49 51 + 2 Rep. 7% 50 50 Even * 13% 51 49 + 2 Dem. 7% 52 48 + 4 Dem. 3% 53 47 + 6 Dem. 1% 54 46 + 8 Dem. <1% 55 45 + 10 Dem. <1% Current * Vice President Joe Biden, Democrat, breaks ties in the Senate. Simulations assume that Greg Orman, the independent candidate in Kansas, will caucus with the majority party.

Several other organizations perform similar calculations. Some use similar statistical models; others rely on reporting and knowledgeable experts’ opinions. We compile and standardize them every day into one scoreboard for comparison. View all states or see how the ratings have shifted over time

Below, a compilation of the latest shifts in Senate race ratings — both in our model and in others.

Based on incumbent winning percentages in previous Senate elections, we’d expect about three incumbents to lose their seats this year – these are the five most likely to fail to be re-elected.