If you’re already a homeowner, do you wonder why you keep getting unsolicited snail mail asking if you have any interest in selling your home? Wonder no more. The gains in home prices are getting bigger as the supply of homes for sale gets leaner, and buyers and their agents are hoping-hoping-hoping you’ll consider selling now instead of later.

According to real estate broker Redfin, the median price of a home sold in March surged 8.9 percent compared with March 2017 —the biggest annual increase in four years. Redfin tracks prices in 174 local markets and calculated the median home price at $297,000.

Like sports cars built in limited supply, low-low home inventories are pushing prices higher. Housing supply was down 11.9 percent in March compared with a year ago. As a result, sales fell 3.7 percent. The number of new listings in March dropped 5.6 percent annually. 

Redfin credits this to sellers being slow to list and new construction failing even to come close to closing the gap. If this does not change, inventory will be a persistent drag on sales for the remainder of the year.

Single-family home construction fell 3.7 percent in March, and building permits, an indicator of future construction, declined 5.5 percent, barely 2 percent higher compared with a year ago. Multifamily construction is one of the few bright spots in all this having increased considerably. Builders are banking on continued, strong demand for rental apartments as homebuyers struggle to find affordable homes.

Despite higher prices, buyer demand is still strong. Sellers, however, are slow to sell because of concerns about finding anything else they like or can afford as well as losing their low fixed mortgage interest rates. With multiple offers being the rule and not the exception to it throughout most larger urban areas, the average home went under contract in 43 days in March, more than a week faster compared with a year ago and a March record. Nearly a quarter of the homes sold for more than their list prices.

Large metropolitan markets in California, Seattle, and Denver continue to see big price gains, but some unexpected markets are seeing inflation as well. Markets like Allentown, PA (21.8 percent), Detroit, MI (20.6 percent) and Las Vegas, NV (16.5 percent) are not far behind.

The supply situation is most acute in Washington, D.C., where inventory fell 22 percent in March annually, according to expert sourced. It would take just 1.8 months at the current sales pace to exhaust the supply. A balanced market supply is considered to be about six months.

With the Feds expected to raise mortgage rates several more times in 2018, current homeowners will have even less incentive to sell. Sales have been dropping as a result of the tight supply, and prices usually lag sales by a few months. That does not appear to be the case, however, in this cycle, as demand is outweighing everything else.