The calendar is looking favorable for Republican presidential candidate Mitt Romney next month. But if Rick Santorum is able to stay in the race, May could be a good month for him.

Six of the eight primaries in April are in the Northeast, where Romney, the former governor of Massachusetts, does well. Maryland and Washington, D.C. primaries are on April 3, and Connecticut, Delaware, New York and Rhode Island are on April 24.

Romney is also currently favored to win Wisconsin's April 3 primary, according to University of Virginia political science professor's Larry Sabato, Kyke Kondik and Geoffrey Skelley. The only state Santorum is currently favored to win in April is Pennsylvania, his home state, on the 24th.

In May, however, the situation is reversed. Santorum will likely do well in six of the eight contests that month: Indiana, North Carolina and West Virginia on May 8, Arkansas and Kentucky on May 22, and Texas on May 29.

Nebraska is considered a "tossup" by Sabato, Kondik and Skelley, and Romney is favored in Oregon. Both of those states will hold a primary on April 15.

Sabato, Kondik and Skelley "guesstimate" that Romney will win an additional 268 delegates and Santorum will win 117 delegates between now and the end of April. According to The Associated Press calculations, Romney currently has 495 delegates to Santorum's 252 delegates.

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If the projections are correct, Romney would have 763 delegates before heading into his May dry spell.

Romney will likely win California's 172 delegates and New Jersey's 50 delegates on June 5, and Utah's 40 delegates on June 26, the last contest. This means that Romney would need to pick up an additional 119 delegates in the remaining states to get the 1,144 delegates need to clinch the nomination.

While Romney has a difficult path ahead, for Santorum it is nearly impossible to get enough delegates to win the nomination before the Republican convention in August, according to Josh Putnam, assistant professor of political science at Davidson College and author of the FrontloadingHQ blog.

The only way for Santorum to win the nomination, therefore, is to deny Romney the delegates needed to win and hope that the delegates will choose him on the second, or a subsequent, ballot during the convention.

The next contests will be the Missouri caucus on Saturday, the Puerto Rico primary on Sunday, and the Illinois primary on Tuesday.