Nassau County extended the grievance deadline by about a month for residents wishing to challenge their taxes – and spending some time online could save people big time.

Eileen Diener was billed more than $16,000 this year in property taxes for her two-story home in North Bellmore. But it's possible she'll end up paying less, perhaps much less. That's because today, spending less than 10 minutes on the official Nassau County Government website, she grieved her taxes.

Jeff Gold, a former member of the Nassau Board of Assessors, is on a one-man mission of sorts to get as many people as possible to grieve their taxes for free instead of paying expensive tax assessment firms. Gold says about 200,000 Nassau residents have grieved their taxes so far this year. A few weeks ago, County Executive Laura Curran extended the deadline to file a grievance to April 2. 

MORE: Jeff Gold stops by News 12 to discuss what you need to know to about tax grievances

“I think everyone needs to file a tax grievance until the county gets it right,” says Gold. “I do believe everyone can do this for free. If you can read instructions, it's very simple.”

Since 2010, 61 percent of the county's property owners have appealed their tax assessments.  As a result, their taxes went up on average only about 5 percent. That’s compared to a 35 percent increase for those who didn't grieve - many of whom come from less affluent, often minority neighborhoods, as Newsday reported last year in a special series, Separate and Unequal.

That’s why Gold is urging property owners who haven't done so already to go online and grieve.

“People who don't grieve are at a huge disadvantage,” says Gold. “It's just a matter of fairness.”