When it comes to life insurance rates, it stands to reason that a group with lower life expectancy (say, men) would have to pay higher premiums than a group that generally lives longer (say, women). But did you know that on average, men pay 38 percent more than women for the same life insurance policy?

That figure comes from InsuranceQuotes.com, which adds that the premium gap widens as the insurer ages. For example, InsuranceQuotes.com found that a 25-year-old man pays 25 percent more than a woman his age for the same policy. At age 45, however, men will pay nearly one-third more than 45-year-old women, while at age 65, the difference grows to 40 percent.

But although few people would likely undergo a sex-change operation just to get lower insurance premiums, you still have a way of trimming premium costs. "You can save a lot of money by getting life insurance while you're young," Laura Adams, a senior analyst with insuranceQuotes.com, said in a press statement.

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"By locking in a level-term policy in your twenties or early thirties," she continued, "you will benefit from much lower rates while protecting your loved ones for decades to come."

Smokers are another group that will have to pay more than average for coverage. But the same trend of dramatically rising rates as you age also applies to smokers.

According to the report, smokers on average pay more than three times as much as nonsmokers for the same insurance policy. For example, a 45-year-old nonsmoking woman will pay about $45 per month for $500,000 of 20-year, term life insurance coverage, but a female smoker the same age pays $167 monthly. That adds up to an annual difference of $1,464 between the smoker and nonsmoker in policy costs.

And while women tend to outlive men, the life expectancy for men in the U.S. has increased at a greater rate than for women.

According to a study by the University of Washington's Institute for Health Metrics and Evaluation, female life expectancy in the U.S. rose from 78 years in 1985 to 80.9 years in 2010, while for men it went from 71 to 76.3 years during that same time period. Even though men are gaining on that score, they're still paying the price when it comes to life insurance.