Just 50% of UK motorists check their car insurance premium at renewal, leaving them out of pocket by up to £225.
Some 8.8 million drivers rolled over their last car insurance policy without shopping around for cheaper options, research from Gocompare.com has found.
Nearly half of the 8.8 million (46%) who allowed their cover to automatically renew did so because they thought as their insurer was the cheapest option last time, it was likely to represent good value for money this time too.
The results comes as the Association of British Insurers (ABI) this week outlined proposals that would see insurers obliged to include the premium customers paid last year and the new quote, making it easier for people to compare prices.
Gocompare.com found there was support from drivers for this, with a quarter (26%) of motorists saying insurers should make it clearer how the renewal price has changed from last year.
One in ten (11%) said insurers used underhand tactics to get customers to renew.
Lee Griffin from Gocompare.com car insurance said the move by the ABI, said: "We need a complete review of the way renewals are handled currently so that consumers feel more in control of the process.
"Many insurers will automatically renew your insurance unless you contact them to tell them otherwise, and their renewal letter will focus on the convenience of needing to do nothing at all in order for your insurance to continue.
"Therefore, beyond just providing customers with last year's premium, we need to ensure the focus is on a proper review of the customers' situation rather than an assumed auto-renewal."
He said options at renewal should be clearly presented and the tone and the language used should reassure consumers that any changes or a switch to another insurer will be handled quickly and willingly, and in a joined-up fashion.
Meanwhile, the impact on family finances of running a second-hand car has also been revealed.
The Money Advice Service has found that 56% of second-hand car owners find that their running costs are higher than expected, while nearly a quarter (23%) said that an unexpected hefty bill has had a big impact on their finances in the past year.
Some 20% have fallen into debt because of the costs of running their vehicle and 39% have been left worried to due to the unforeseen repair costs.
It is advising people to think about the true costs of their car before they drive away, with 28% forgetting to consider the cost of an MOT when they bought a car and 16% didn't think about car tax. A quarter (26%) found fuel costs to be high than they expected, while
23% thought their insurance was surprisingly expensive.