T. Rowe Price has included a college investment calculator on its Web site to help families figure out how much they will need to invest in a 529 plan. The calculator examines the probability of various portfolios in 500 scenarios.

The College Board estimates that the current average annual cost at a private college is $24,946. Assuming an annual 5% inflation rate, the average cost for four years at a private college will reach $261,300 by 2020, according to The College Board.

T. Rowe Price's calculator indicates that parents of a child born today would need to save $846 each month over the next 18 years to put that child through private college. With The College Board estimating that the average cost for four years at a public college will reach $118,800 by 2020, T. Rowe Price's 529 calculator indicates that parents would need to save $313 a month to put a child born today through a public college by 2020.

The calculator can also project future costs at specific schools and can account for expected financial aid.

"Saving for college is a primary goal for a large number of American families. Parents need help calculating how much they need to save," said Todd Cleary, head of financial planning for T. Rowe Price.

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