A European Union ban on insurers using gender to set prices, which comes into force today (21 December), will likely lead to higher insurance costs for consumers.
The EU's highest court outlawed insurers' practice of charging men and women different prices as sex discrimination in March 2011 after Belgium's consumer association brought a test case against it.
The move has drawn criticism from insurers who say gender exerts a strong influence over how likely a person is to claim, and should be reflected in the premiums they pay.
Higher prices would be welcomed by a European insurance industry squeezed by rock-bottom interest rates and recession in several key markets.
Insurers typically charge lower prices for women drivers because they are statistically less likely to crash than men.
They also offer male retirees who buy annuities – investment policies that pay a regular income for the remainder of the customer's lifetime – more generous payments than women because men die sooner, on average.
The biggest changes were expected in the motor insurance market where women below the age of 25 will, from Friday, pay up to 40% more to eliminate the discount they enjoy relative to men, accountants PricewaterhouseCoopers estimated.
Insurers won't match the increases in female motor premiums with lower rates for male drivers, boosting revenues, although the gain will be competed away over time, said Björn Norrman, an analyst at credit rating agency Fitch.
"I would assume that in the beginning you will see much more increases for younger female drivers than you will see decreases for young male drivers," he said.
Insurers seeking to comply with the ban face a choice between introducing a "unisex" rate pitched between the higher and lower prices they currently charge, or by bringing the lower rate into line with the higher one.
Insurers could also try to sidestep the ban by basing their pricing on proxy gender indicators such as the customer's profession or model of car, although this would be vulnerable to legal challenges, law firm Eversheds said.
The ban was also expected to boost demand for so-called telematics insurance, where insurers monitor customers' behaviour through devices installed in cars, and charge according to how riskily they drive, irrespective of gender.
Europe's biggest motor insurers include Allianz, Axa, Direct Line and Generali.