I get a lot of people asking how accurate Zillow is at their Zestimates. The answer for our county is “Not very”.

As of 3/10/10, only 18% of closings in SLO county were within 5% of the Zestimate; 34% within 10%, and 58% within 20%. That means that 42% of the Zestimates were over 20% off the actual value, and 66% were at least 10% off the true value as shown by an actual closing.

The median error is 16% in SLO County. The best accuracy in the state is Ventura with a median error of 10.5%.

This info is from Zillow itself. Please check out the following link.

http://www.zillow.com/howto/DataCoverageZestimateAccuracyCA.htm