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 Aug 1, 2010 is about 8.5 months, just looking at single family homes, about 7.7 months.

	County	Status & Est Inventory	TYPE OF LISTING				TOTAL
			Single Family	Single Family with Acreage	Condo	Townhouse
	Ada	Sold	6199	242	191	285	6917
		Active	3305	237	317	263	4122
		Pending	713	33	16	28	790
		Inventory*	7.8	13.4	20.9	12.3	8.5
	Canyon	Sold	2900	346	1	48	3295
		Active	1529	351	1	48	1929
		Pending	321	45	0	6	372
		Inventory*	7.7	13.7	12.0	13.5	8.4
	*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	4018	6199	7.8	3429	7.0	1509	8.0
	Canyon	Several	1850	2900	7.7	1577	7.0	721	7.7
	Gem	Several	103	124	10.0	68	9.1	40	7.7
	Elmore	Several	276	230	14.4	128	12.9	67	12.4
	Payette	Several	207	152	16.3	87	14.3	49	12.7
Single Family Only - Date Range: 9/1/2009 - 8/31/2010. 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	271	319	10.2	181	9.0	87	9.3
		200	85	141	7.2	80	6.4	39	6.5
		300	252	431	7.0	232	6.5	97	7.8
		400	275	340	9.7	187	8.8	79	10.4
		500	125	167	9.0	88	8.5	25	15.0
		550	374	630	7.1	332	6.8	153	7.3
		600	192	265	8.7	154	7.5	75	7.7
		650	420	609	8.3	370	6.8	158	8.0
		800	271	358	9.1	205	7.9	88	9.2
	Eagle	900	274	394	8.3	231	7.1	94	8.7
	Star	950	129	198	7.8	118	6.6	59	6.6
	Meridian	1000	190	257	8.9	134	8.5	64	8.9
		1010	36	65	6.6	41	5.3	16	6.8
		1020	328	573	6.9	297	6.6	134	7.3
		1030	540	929	7.0	527	6.1	227	7.1
	Kuna	1100	236	488	5.8	219	6.5	81	8.7
Canyon	Nampa	1250	318	538	7.1	290	6.6	129	7.4
		1260	495	695	8.5	386	7.7	179	8.3
		1270	321	478	8.1	262	7.4	119	8.1
	Melba	1265	8	10	9.6	7	6.9	4	6.0
	Caldwell	1275	122	229	6.4	123	6.0	52	7.0
		1280	383	657	7.0	340	6.8	152	7.6
	Middleton	1285	132	205	7.7	111	7.1	55	7.2
	Other	1290	28	22	15.3	11	15.3	6	14.0
Single Family Only - Date Range: 9/1/2009 -8/31/2010. Intermountain MLS
County	City	Price Range	Active	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	401	434	11.1	303	7.9	154	7.8
		$100,00 - $199,999	2237	3833	7.0	2087	6.4	854	7.9
		$200,000 - $299,999	793	1213	7.8	653	7.3	314	7.6
		$300,000 - $449,999	386	481	9.6	259	8.9	121	9.6
		$450,000 - over	196	132	17.8	74	15.9	42	14.0
Canyon	Several	$0 - $99,999	943	1559	7.3	922	6.1	432	6.5
		$100,00 - $199,999	763	1214	7.5	597	7.7	272	8.4
		$200,000 - $299,999	109	86	15.2	40	16.4	14	23.4
		$300,000 - $449,999	25	24	12.5	7	21.4	0	#DIV/0!
		$450,000 - over	5	1	60.0	1	30.0	1	15.0
	**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	314	273	13.8	148	12.7	76	12.4
	Canyon	Several	399	375	12.8	216	11.1	107	11.2
	Gem	Several	99	71	16.7	46	12.9	23	12.9
	Elmore	Several	68	34	24.0	20	20.4	8	25.5
	Payette	Several	102	46	26.6	29	21.1	12	25.5
Single Family with ACREAGE - Date Range: 9/1/2009 - 8/31/2010. Intermountain MLS
County	City	Price Range	Active	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	6	9	8.0	6	6.0	2	9.0
		$100,00 - $199,999	26	49	6.4	28	5.6	11	7.1
		$200,000 - $299,999	38	61	7.5	39	5.8	22	5.2
		$300,000 - $449,999	89	77	13.9	44	12.1	23	11.6
		$450,000 - over	154	68	27.2	26	35.5	14	33.0
Canyon	Several	$0 - $99,999	27	38	8.5	29	5.6	17	4.8
		$100,00 - $199,999	128	133	11.5	77	10.0	37	10.4
		$200,000 - $299,999	119	142	10.1	83	8.6	36	9.9
		$300,000 - $449,999	85	57	17.9	26	19.6	17	15.0
		$450,000 - over	38	4	114.0	1	228.0	0	#DIV/0!