College tuition in the United States rises faster than nearly everything else -- roughly 5 percent a year at many private schools, double the general inflation rate. A newborn's future diploma is therefore a moving target, and guessing a monthly savings number without doing the math almost guarantees coming up short. This calculator projects both sides of the race: how your savings grow, and how the price tag grows.

Start with your child's current age and the age they will start college. The tool compounds your current savings and monthly contributions at your expected return, usually from a 529 plan invested in stock index funds. Separately, it inflates today's annual college cost at the college inflation rate you enter, then multiplies by four years. The gap between the two projections is the number that matters.

Suppose your daughter is 5, you have $5,000 saved, and you contribute $300 a month earning 6 percent. By age 18 the account holds roughly $78,000. But a school costing $25,000 a year today costs over $47,000 a year by then, or about $188,000 for four years. The calculator shows the shortfall and the higher monthly contribution needed to close it, so you can adjust while compounding still has a decade to work.

With the pre-filled defaults — Child's Current Age 5, College Start Age 18, Current Savings $5,000, Monthly Contribution $300, Expected Return 6%, College Cost Inflation 5%, Current Annual College Cost $25,000 — the College Savings Calculator returns Years Until College 13, Projected Savings at College Start $78,640.34, Future Annual Cost $47,141.23, Total 4-Year Cost $188,564.91, Savings Gap $109,924.58, Required Monthly to Close Gap $485.13. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.