Up to 50% of all homeowners in Fresno County who bought their houses within the last three years may be over paying on property taxes, according to a research by a San Diego software company.

Families who bought their properties at the peak of the real estate market between 2005 and 2007 have likely seen the values decline. As a result, they could potentially save an average of $368 to $401 per year if they get the properties reassessed, said Adam Berkson, president and co-founder of EasyTaxFix.com, which crunched data and developed a formula for homeowners in San Diego and Fresno counties.

EasyTaxFix uses information from MDA DataQuick, which tallies home sales and pricing information statewide, to develop a program that calculates the likelihood of an over assessment on their property.

The county has already reassessed 46,500 properties -- most single-family homes -- bought since 2004, which is when the run-up in values started. Those properties have declined in value a total of $2.5 billion.

Homeowners who think their homes should be reassessed can file applications for free with Fresno County or pay $39.99 for EasyTaxFix.com to do it.

Berkson came up with the service when he tried to get his house in San Diego reassessed and found the application process daunting. It required him to get "comp" sales in his neighborhood, which proved more difficult than he thought.

EasyTaxFix.com uses recent sales in the neighborhood to calculate whether the house might be over assessed. I tested it with my home, which was purchased in 1993. I typed in the address and zip code and hit the "continue" button.

"No savings" it said.

Which is what I expected. We bought it way before real estate values skyrocketed and have built up 15 years of equity. Values have to fall absurdly low for us to be under water.

Berkson said he would expect no more than 15% of all residences in Fresno County be under assessed, although that percentage increases if only the residences bought at the peak of the market are counted.

EastTaxFix.com is available only in San Diego and Fresno counties, but will likely be expanded next year. Why those two counties: Berkson lives and has an analytics business in San Diego, and has a client in Fresno.