The cost of auto insurance varies depending on the month you purchase a policy, according to a yearlong study of 2013 monthly insurance premiums conducted by The study analyzed the average rate for a new full-coverage auto policy for a 35-year-old single male driver with a $500 deductible and a clean driving record in each U.S. state and Washington, D.C. says the study found that December was the least expensive month to purchase auto insurance both nationally and in Arizona, Alaska, Colorado, Georgia, Hawaii, Idaho, Indiana, Maine, Maryland, Minnesota, Montana, New Hampshire, New Mexico, New York, Oklahoma, Pennsylvania, South Carolina, Texas, Vermont, Virginia, Wyoming and Washington, D.C.

Meanwhile, March was the most expensive month to purchase auto insurance both nationally and in Alabama, Arizona, Alaska, Delaware, Georgia, Hawaii, Illinois, Kansas, Louisiana, Massachusetts, New Jersey, South Carolina, Washington, Washington, D.C., West Virginia and Wisconsin.

However, while December was the cheapest month nationally, it was also the most expensive in 11 states. The study notes that the rates vary state to state depending on how strict rate regulation is in each state and the “unique ebb and flow” of every insurance company.

The chart on the right shows the ranking of all 50 states and Washington, D.C. based on the greatest median price difference between the least expensive and most expensive months to purchase auto insurance. (Click to enlarge.)

Read more about the study from Nick DiUlio HERE.