by Calculated Risk on 7/21/2010 12:08:00 PM

Earlier I mentioned that a normal housing market usually has under 6 months of supply. The NAR reported that months of supply was at 8.3 months in May, and the months of supply was probably be higher in June (to be reported tomorrow).

A quick estimate: If sales are 5.3 million (SAAR) in June, and inventory stays the same at 3.9 million units, the months of supply will rise to 8.8 months in June.

This is calculated as: 3.9 divided by 5.3 * 12 (months) = 8.8 months of supply.

For July, if sales fall to 4.5 million (it could be lower) and inventory is still at 3.9 million units, months of supply will rise to 10.4 months.

I think these estimates are conservative (actual will probably be higher). For reference, the all time record high was 11.2 months of supply in 2008.

This level of supply will put additional downward pressure on house prices.

Click on graph for larger image in new window.

This graph show months of supply and the annualized change in the Case-Shiller Composite 20 house price index.

Below 6 months of supply (blue line) house prices are typically rising (black line).

Above 6 or 7 months of supply house prices are usually falling (although there were many programs to support house prices over the last year).

The dashed red line is the estimate for months of supply in June and July.

This is a key reason why I expect house prices to fall further later this year as measured by the Case-Shiller and CoreLogic repeat sales house price indexes.