Women drivers could see their insurance premiums increase by around 25% as new laws come into force that ban setting prices according to gender.
The European Court of Justice ruling follows a 10-year legal battle against the proposals by insurers.
The change is not confined to car insurance but also covers pensions and life insurance.
Women have benefited from smaller car insurance premiums due to their lower accident rates, but predictions of how they will be affected vary widely.
Some analysts believe younger women could see their premiums almost double, with average rises of around £300 a year.
Those aged between 31 and 35 are also likely to be hit with a rise of around 10%, or £53 a year, according to research from comparison website Confused.com.
Michael Ossei, personal finance expert at price comparison website uSwitch, told Sky News that women aged between 18 and 25 will be heavily affected by the change.
More than a third of the women the website had surveyed would have to cut back their living expenses to cope with higher premiums and one in 10 may end up selling their car.
Others, though, forecast the increases could be gentler than expected, provided insurers can piece together enough information about someone as a driver.
Kevin Pratt, insurance expert at the MoneySupermarket website, said he hopes insurers will place greater emphasis on factors such as job, type of car, driving record, any security measures on the car and age to make sure drivers can still get a reasonable price.
The new rules could also hit men reaching retirement, with annuities possibly decreasing by up to 13% a year. Women may see their life insurance policies increase by 16%.
Currently, men usually get a higher pension income than women because, on average, they die younger.
The Government is strongly opposed to the change.
Transport Minister Stephen Hammond told Sky News it was unnecessary and that they were working to manage the impact.
"One of the reasons we are against it (is that) the basic principles of insurance previously has been insurance based on risked rather than just gender-based."
The court ruling is an attempt to end discrimination and to bring about equality between men and women - but it is a decision that will come at a price for many.