SEATTLE—Redfin has a report showing an increase of just 0.3% to 93 in September 2015 from 92 a year earlier, the smallest annual increase so far this year.

The Redfin Housing Demand Index is the industry's first and only measure of homebuyer activity prior to purchase, and is based on millions of visits to Redfin.com home-listing pages and thousands of Redfin customers requesting tours and writing offers in 15 major metro areas.

In September, the number of Redfin customers writing offers was up 10% from last year for the second month in a row. Meanwhile, growth in the number of customers requesting home tours slowed to 23% from 31% in August. That's a change from the summer when Redfin reported that more people were touring homes but fewer were making offers.

Redfin says this change suggests that homebuyers are still out there, but they're frustrated by a lack of choice and high prices. Although new listings are up 5.1% from last year, the overall inventory of homes for sale is down 2.8%. The typical home in October sells a week faster than it did a year ago. Redfin's forecast model, the industry's earliest forecast of U.S. home values and sales across 15 major metro areas, shows a 4.5% increase in prices year-over-year and a 7.3% rise in sales in October. Redfin projects that in November home prices will rise 4.3% and sales will advance 8.3%. “We're bullish on sales for the remainder of 2015,” says Nela Richardson, Redfin chief economist. “Though we think buyers have had enough of over-the-top pricing.” The key question is how long new listings will continue to drive sales. The bear case is that the combination of woefully low inventory and high prices could take its toll on buyers and cause sales to shrink, The bull case is that sellers are in the best position they've been in years to make a move, be it trading up, downsizing or cashing out. At $12.1 trillion, U.S. home equity is at the highest level since 2006. Today's rock bottom mortgage rates can help keep monthly payments within an affordable range for sellers who want to trade up. There's also evidence that loans are becoming easier to come by, which could boost sales at year-end. In September, the median sale price in the 15 metros that compose the Demand Index increased 4.8% from a year earlier. Redfin had forecasted for 5.3% growth. September sales were up 10.5% year over year against the forecast of 10%. To read the full report, complete with data, charts, insights and a full methodology, click here.