The fuzzy math of auto insurance rates

We all know (some of us the hard way) that being a good driver helps lower your auto insurance premiums. But lots of other factors are involved as well -- some of which you have no control over and have nothing to do with how well you drive.

For one thing, it helps a lot if you're a woman. Over the course of their lives, guys pay about $15,000 more for auto insurance than women, according to CoverHound.com, an insurance shopping service. But the differences can be even more dramatic depending on your age, location and other variables.

A new report from InsuranceQuotes.com looked at how much impact age, gender and marital status have on the cost of car insurance. It found a lot of variability.

The biggest gender difference is among younger drivers. For the same policy, single 20-year-old women pay on average 23 percent less than similarly situated men.

That's is because men are 10 percent less likely to wear a seatbelt than women, more than three times as likely to be arrested for driving under the influence and, in fatal accidents, speeding was 9 percent more likely to be a factor when men were driving than when women were.

But the premium gap narrows significantly by age 30. From then to age 65, single men actually pay about 1 percent less than single women.

Although married men and women pay almost the same amount between ages 30 and 65, they pay substantially less than their single counterparts. Married 20-year-old men and women pay an average of 26 percent less than unmarrieds. That drops to about 5 percent less by age 30 and then stays from 2 percent to 4 percent less from then until age 75.

Don't worry about paying a lot more if you become single again. CoverHound reports getting divorced means your auto insurance will go up, on average, just 1.21 percent.

Education is another factor. Over the course of a lifetime, a high school dropout will pay an average of $712 more than a high school graduate, $2,154 more than a college graduate and $2,164 more than someone with a doctorate, according to CoverHound. But it depends entirely on which insurer you choose. About 40 percent of insurers don't consider education when setting rates.

While some statistics suggest a correlation between education and good driving, several states have challenged this metric, including New York, New Jersey and Rhode Island.

Having or not having a job doesn't do much to your insurance costs, but what you do with your money does. While credit scores and driving records have no correlation, insurance companies use credit scores as an indicator of who is most likely to pay their premiums. California has banned this practice.

As in real estate, insurance costs depend on location. The average annual cost for a driver in Michigan, the state with the highest rates, is $2,551, according to Insure.com. However if that same driver goes to neighboring Ohio, which has the lowest rates, he or she will only pay $926. Indiana, another state bordering on Michigan, has the 40th-lowest average cost, and there that driver would be paying $1,200 a year.

As you can see, different states have different rules about what can and can't be used to set your insurance rates. Check with your state insurance department to find out what the law in your state allows.

  • Constantine von Hoffman On Twitter»

    Constantine von Hoffman is a freelance writer and writing coach. His work has appeared in outlets such as Harvard Business Review, NPR, Sierra magazine, Brandweek, CIO, The Boston Herald, TheStreet.com, CSO, and Boston Magazine.