Last week Zillow released its second quarter Negative Equity Report. The report shows that nationally the negative equity rate had fallen to 30.9 percent from 31.4 percent in the first quarter and that half of all borrowers under 40 were underwater on their home loan.

Today Zillow is reporting the percentage of homeowners under 40 years old who are underwater on their mortgage for the 100 largest metro areas covered by the report (chart below).

This is an important number to consider when looking at the pipeline of sales. As Stan Humphries, Zillow’s chief economist, put it in a recent interview, “homeowners under 40 who are stuck in negative equity are gumming up the treadmill. They can’t move into larger homes, and those looking for entry level homes have little inventory to choose from.”

Of course, renting is always an option for homeowners who are unable to sell, and Zillow has tools for people in that situation. You can check out median rents (going up in most places) on the Zillow Real Estate Market Reports, as well as your home’s own Rent Zestimate, to help you price your home for rent, then post your home for rent, for free, on Zillow.

But, if renting out your home is not something you’re interested in, you should at least consider refinancing, especially if your current rate for a 30-year fixed mortgage is above 4.5 percent. And yes, in most instances you can refinance your underwater home loan. Zillow Mortgage Marketplace can now quote for HARP 2.0 and FHA Streamline Refinance (underwater loan program) so be sure to check it out.

In the meantime, take a look at the alphabetical list of the percentage of homeowners under 40 who are underwater on their mortgage. The list ranges from 23.3 percent in the Rochester, NY metro area all of the way up to 81.4 percent in the Las Vegas, NV metro.