Months of Inventory, Explained: How to Read Seattle Supply Stats
Months of inventory is the most-quoted housing stat after price. Here's how it's calculated, what the thresholds mean, and the ways it can mislead you.
If you read one housing statistic beyond price, make it this one. Months of inventory (also called months of supply, or MOI) is the closest thing the housing market has to a single balance gauge — and it’s quoted constantly in Seattle market commentary, usually without explanation. This post is the explanation: what the number is, how it’s built, what the conventional thresholds mean, and the specific ways it can fool you.
What the number actually is
Months of inventory answers one question: at the current pace of sales, how long would it take to sell every home currently on the market if nothing new were listed?
The standard calculation:
Months of inventory = active listings ÷ closed sales per month
As an illustrative example: if a market has 2,000 active listings and homes are closing at 1,000 per month, it has 2.0 months of inventory. If sales slow to 500 a month with the same listings, supply doubles to 4.0 months — without a single new home hitting the market. That’s the first thing to internalize: MOI is a ratio. It moves when supply changes, when demand changes, or both, and the number alone won’t tell you which.
The conventional thresholds
These cutoffs are rules of thumb, not laws of physics — but they’re the shared vocabulary the industry uses, so they’re worth knowing:
| Months of inventory | Conventional label | What it tends to feel like |
|---|---|---|
| Under ~3 months | Seller’s market | Multiple offers, fast pendings, prices firm or rising |
| ~3–6 months | Balanced market | Negotiation in both directions, normal days on market |
| Over ~6 months | Buyer’s market | Price cuts, contingencies accepted, prices flat or soft |
One crucial piece of local context: Seattle has spent most of recent memory well below the “balanced” range. In-city and Eastside single-family supply has often measured in weeks, not months. That recalibrates what the numbers mean here in practice — a reading that would be unremarkable nationally can feel like a flood locally, and a move from one month to two can change the on-the-ground experience dramatically even though both are nominally “seller’s market” territory. In supply-starved markets, the change matters more than the level.
How to read it without getting fooled
MOI is genuinely useful, but it has failure modes. Here are the ones that matter most in Seattle.
1. It blends segments that behave like different markets
A single county-wide MOI averages together downtown condos, Ballard craftsmans, and Sammamish five-bedrooms — segments that can be moving in opposite directions at the same time. Seattle’s condo and single-family markets, in particular, often diverge sharply (we cover why in the condo vs. single-family divergence). Always ask: months of inventory of what, where? A price-band or property-type breakdown beats the headline number every time.
2. It’s seasonal, like everything else
Inventory builds through spring and summer and drains through winter — every year, regardless of market direction. A rise in MOI from March to July is the calendar, not a trend. Compare year over year (this March vs. last March), the same discipline we recommend for every stat in Seattle housing market seasonality.
3. The denominator looks backward
Closed sales reflect deals struck four to six weeks earlier, so MOI built on closings is a slightly stale photo. When a market turns quickly, MOI lags the turn. Sharper readers swap in pending sales as the denominator — pendings are the freshest demand signal available — or simply watch pendings alongside MOI as the early-warning system.
4. Active listings hide their composition
Two markets can show identical listing counts where one is fresh inventory and the other is accumulated stale listings that buyers have already rejected. Pair MOI with median days on market and the share of listings with price reductions to tell the difference. Rising MOI with rising DOM and spreading price cuts is a genuine cooldown; rising MOI with fast pendings just means more sellers showed up to a still-hungry market.
5. Thin data makes noisy ratios
For a single neighborhood, the monthly sales count can be small enough that one slow month swings MOI wildly. At the neighborhood level, treat any single month as anecdote and look for three consecutive months pointing the same way before calling it a trend.
A worked habit: the three-question read
When you see a months-of-inventory figure quoted, run it through three questions:
- Compared to the same month last year, is it higher or lower? (Filters out seasonality.)
- Did the numerator move, the denominator, or both? More listings is a different story than slower sales, and the combination is a different story again.
- Does the segment I care about match the headline? Check your property type and price band before applying a county-wide number to your own decision.
Three questions, thirty seconds, and you’re reading the stat more carefully than most of the people quoting it.
Where MOI fits in the bigger dashboard
Months of inventory is the balance gauge; it’s at its best alongside the speed gauge (days on market) and the intensity gauge (list-to-sale price ratio — which in Seattle requires its own decoder, given how often homes here sell over list price). For the full instrument panel and how the pieces fit together, see how to read market stats like an agent — and for these indicators applied to a real month, our April 2026 market update.
The honest take
Months of inventory is the single best one-number summary of market balance — and like every one-number summary, it’s most dangerous when treated as self-explanatory. Know the formula, respect the thresholds as conventions rather than truths, and always check the year-ago comparison before drawing conclusions.
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