Appraisers call this Absorption Rate! The numbers below would be similiar for the 1004MC form appraiser use.  (Learn more). 

Another method is simple inventory, however it assumes all the active inventory will sell, which it does not. Therefore this method will slightly overstate the inventory, but is more accurate than using the DOM, or Cumulative DOM as reported in MLS.  This method also counts the days from "Off Market" to "Close Date", however it will ALWAYS do this, therefore the trend is the same.  

MLS will provide the DOM of typically the LAST listing, not the 3 or 4 prior listings. This is more apparent in a downward market.  I would like to share detail examples, but it violates IMLS rules and regulations. (per IMLS)  However, agents which have access to IMLS can search the following addresses to understand the issue more.   Or just do this very simple search, let MLS tell you the Average DOM for SOLD for 6 months, they look at the same search filter, but ACTIVE.  The ACTIVE DOM right now will be 50 - 60% higher!

      1) 2301 W Hillway
      2) 7490 N Waterlilly Ave. 
      3) 25933 Chandler Drive 
      4) 3272 S Quarterswing Way
      5) 2030 W Havenwood Ave
      6) 1862 Grand Teton
      7) 12458 N Upper Ridge
      8) 304 S Rivermont Ln

Inventory is one key in understanding if a market is adding, reducing or holding steady. Inventory impacts days on the market (DOM), inventory along with the average sales price and average sales ratio are tools to understand the market.

Were does Ada County stand? Depends on what market.  Ada County overall inventory as March 1, 2010 is about 9.6 months, just looking at single family homes, about 9.0 months.

Reviewing just Single Family, last 3 months been tracking around 8.4 months inventory, based on 12 month prior sales.  

	Data Source : Intermountain MLS
	Report Date: March 1, 2010
	Date Filter: 3/1/2009 - 2/28/2010
	www.hennesseyappraisals.com
	County	Status & Est Inventory	TYPE OF LISTING				TOTAL
			Single Family	Single Family with Acreage	Condo	Townhs
	Ada	Sold	5655	207	146	285	6293
		Active	3441	210	277	236	4164
		Pending	786	37	24	39	886
		Inventory	9.0	14.3	24.7	11.6	9.6
	Canyon	Sold	2534	285	0	35	2854
		Active	1682	329	2	45	2058
		Pending	378	56	0	3	437
		Inventory	9.8	16.2	N/A	16.5	10.5
	*Estimated from 12 months sales. 12 Month Sales / (Current Active + Current Pending )= Inventory
	Inventory Units = Months
	Single Family Only
	County	MLS Area	Current Active + Pend Listings	12 Month Sales	Est Inventory using 12 Months Sales (Months)	6 Month Sales	Est Inventory using 6 Months Sales (Months)	3 Month Sales	Est Inventory using 3 Months Sales (Months)
	Ada	Several	4215	5655	8.9	2742	9.2	990	12.8
	Canyon	Several	2053	2534	9.7	1312	9.4	518	11.9
	Gem	Several	91	116	9.4	56	9.8	21	13.0
	Elmore	Several	295	245	14.4	101	17.5	41	21.6
	Payette	Several	190	139	16.4	65	17.5	29	19.7
Single Family Only - Date Range: 3/1/2009 - 2/28/2010. Intermountain MLS
County	City	MLS Area	Active + Pending	12 Month Sales	Est Inventory using 12 Months Sales (Months)	6 Month Sales	Est Inventory using 6 Months Sales (Months)	3 Month Sales	Est Inventory using 3 Months Sales (Months)
Ada	Boise	100	260	287	10.9	137	11.4	41	19.0
		200	79	121	7.8	60	7.9	15	15.8
		300	255	417	7.3	197	7.8	76	10.1
		400	265	345	9.2	153	10.4	53	15.0
		500	112	164	8.2	78	8.6	28	12.0
		550	418	579	8.7	293	8.6	104	12.1
		600	192	212	10.9	111	10.4	34	16.9
		650	431	497	10.4	235	11.0	102	12.7
		800	259	336	9.3	153	10.2	55	14.1
	Eagle	900	309	344	10.8	161	11.5	62	15.0
	Star	950	144	177	9.8	79	10.9	37	11.7
	Meridian	1000	173	244	8.5	122	8.5	45	11.5
		1010	38	51	8.9	24	9.5	12	9.5
		1020	355	538	7.9	273	7.8	107	10.0
		1030	626	863	8.7	396	9.5	154	12.2
	Kuna	1100	283	475	7.1	368	4.6	63	13.5
Canyon	Nampa	1250	332	420	9.5	247	8.1	94	10.6
		1260	527	652	9.7	306	10.3	126	12.5
		1270	370	413	10.8	214	10.4	89	12.5
	Melba	1265	8	9	10.7	3	16.0	2	12.0
	Caldwell	1275	148	211	8.4	107	8.3	42	10.6
		1280	434	605	8.6	312	8.3	120	10.9
	Middleton	1285	149	164	10.9	94	9.5	33	13.5
	Other	1290	29	18	19.3	10	17.4	4	21.8
Single Family Only - Date Range: 3/1/2009 - 2/28/2010. Intermountain MLS
County	City	Price Range	Active + Pending	12 Month Sales	Est Inventory using 12 Months Sales (Months)	6 Month Sales	Est Inventory using 6 Months Sales (Months)	3 Month Sales	Est Inventory using 3 Months Sales (Months)
Ada	Several	$0 - $99,999	239	205	14.0	130	11.0	62	11.6
		$100,00 - $199,999	2519	3523	8.6	1733	8.7	574	13.2
		$200,000 - $299,999	866	1221	8.5	556	9.3	230	11.3
		$300,000 - $449,999	377	474	9.5	220	10.3	91	12.4
		$450,000 - over	210	152	16.6	57	22.1	14	45.0
Canyon	Several	$0 - $99,999	887	1117	9.5	633	8.4	272	9.8
		$100,00 - $199,999	996	1262	9.5	610	9.8	212	14.1
		$200,000 - $299,999	130	105	14.9	46	17.0	22	17.7
		$300,000 - $449,999	29	38	9.2	17	10.2	10	8.7
		$450,000 - over	9	0	N/A**	0	N/A**	0	N/A**
	**N/A = Lack of Sales to Forecast
	Below $99,999 does not included "0SLD" = Zero Sold Price or $1,000 Active (Auction) listings

	Single Family with ACREAGE
	Must have More than 1 Acre.
	County	MLS Area	Current Active + Pend Listings	12 Month Sales	Est Inventory using 12 Months Sales (Months)	6 Month Sales	Est Inventory using 6 Months Sales (Months)	3 Month Sales	Est Inventory using 3 Months Sales (Months)
	Ada	Several	288	231	15.0	123	14.0	55	15.7
	Canyon	Several	399	307	15.6	156	15.3	70	17.1
	Gem	Several	111	52	25.6	25	26.6	8	41.6
	Elmore	Several	57	32	21.4	13	26.3	4	42.8
	Payette	Several	98	41	28.7	17	34.6	7	42.0
Single Family with ACREAGE - Date Range: 3/1/2009 - 2/28/2010. Intermountain MLS
County	City	Price Range	Active + Pending	12 Month Sales	Est Inventory using 12 Months Sales (Months)	6 Month Sales	Est Inventory using 6 Months Sales (Months)	3 Month Sales	Est Inventory using 3 Months Sales (Months)
Ada	Several	$0 - $99,999	2	4	6.0	3	4.0	3	2.0
		$100,00 - $199,999	31	30	12.4	20	9.3	9	10.3
		$200,000 - $299,999	54	44	14.7	22	14.7	9	18.0
		$300,000 - $449,999	71	66	12.9	32	13.3	14	15.2
		$450,000 - over	129	80	19.4	42	18.4	19	20.4
Canyon	Several	$0 - $99,999	18	16	13.5	9	12.0	3	18.0
		$100,00 - $199,999	124	87	17.1	54	13.8	23	16.2
		$200,000 - $299,999	135	125	13.0	58	14.0	27	15.0
		$300,000 - $449,999	81	69	14.1	31	15.7	16	15.2
		$450,000 - over	43	8	64.5	3	86.0	1	129.0
	**N/A = Lack of Sales to Forecast
	Below $99,999 does not included "0SLD" = Zero Sold Price or $1,000 Active (Auction) listings