What it means
The survey asks purchasing managers a short set of questions about new orders, output, employment, supplier delivery times and stocks of purchases, and each answer is simply better, the same, or worse than last month. Those responses are converted into diffusion indices, then weighted together into the headline figure that gets reported.
The 50 line is what makes it so readable. A move from 48 to 52 says conditions have turned from shrinking to growing, and the distance from 50 gives a rough sense of how quickly, without needing any knowledge of the underlying units.
Its real advantage is timing. Official output and trade statistics arrive weeks or months after the period they describe and are then revised, whereas the PMI lands within a few days and rarely changes afterwards, which is why markets often move sharply on the release.
For a business, the sub indices are more useful than the headline. New orders is the forward looking component, employment signals hiring intentions across the sector, and supplier delivery times lengthening is a classic early warning of both capacity pressure and rising input prices.
There are separate manufacturing, services and composite versions, and in most developed economies services is by far the larger part of activity. Reading only the manufacturing PMI in a service dominated economy is a common way to draw the wrong conclusion about overall growth.
Two cautions are worth carrying. The index measures direction rather than magnitude, so a reading of 51 for six months signals steady growth that could still be very slight, and because it is survey based it reflects sentiment as well as fact and can overshoot at turning points.
In practice
Real-world examples.
Example
A steel stockholder watches the manufacturing new orders sub index fall from 54 to 47 over three months. It cuts its own forward purchasing by 20% and avoids being caught with expensive inventory when demand drops.
Example
An investment committee sees the composite PMI cross above 50 for the first time in a year. It rotates part of its portfolio towards cyclical sectors ahead of the official output data that will not be published for another six weeks.
Example
A recruitment agency tracks the employment sub index across services and manufacturing separately. When the services figure holds above 53 while manufacturing sits at 46, it moves consultants off industrial accounts and onto hospitality and professional services clients.
Think of it
“PMI is the abbreviation for Purchasing Managers Index-expansion/contraction indicator.
Formula
Calculation
Diffusion index = (% of respondents reporting improvement) + (0.5 x % reporting no change)
Headline PMI = weighted average of the five component indices
Suppose 30% of purchasing managers report new orders higher than last month, 55% report no change and 15% report a decline. The new orders index = 30 + (0.5 x 55) = 30 + 27.5 = 57.5, comfortably in expansion.
If instead 22% report improvement, 48% no change and 30% a decline, the index = 22 + (0.5 x 48) = 22 + 24 = 46.0, indicating contraction.
Now build a headline figure from five components using the common weightings of 30% new orders, 25% output, 20% employment, 15% supplier delivery times and 10% stocks of purchases. With readings of 57.5, 56.0, 51.0, 49.0 and 48.0 respectively:
(0.30 x 57.5) + (0.25 x 56.0) + (0.20 x 51.0) + (0.15 x 49.0) + (0.10 x 48.0) = 17.25 + 14.00 + 10.20 + 7.35 + 4.80 = 53.6. The sector is expanding, driven by orders and output while employment barely grows and stocks are being run down.Case study
Seen in the real world.
The following is an illustrative and entirely fictional example. Ferngate Components, an invented supplier of fasteners to industrial customers, planned its purchasing on a rolling twelve month average of its own sales. That method worked well in stable periods but always turned late, because its own order book only softened after its customers had already slowed.
A new operations director began tracking the manufacturing new orders sub index alongside the headline PMI. She noticed that this component tended to turn roughly four months before Ferngate's own revenue, and built a simple rule: two consecutive months below 48 triggered a review of forward raw material commitments.
When the index fell to 47.2 and then 46.5, the fictional company cut its next quarter's steel wire orders by a third and shortened its supplier contracts. Demand did fall, and Ferngate carried roughly $900,000 less slow moving stock through the downturn than it had in the previous cycle, freeing cash at exactly the point when its competitors were discounting to clear warehouses.
Watch out
Common mistakes.
- Reading a fall from 58 to 53 as a contraction, when both figures are above 50 and the sector is still growing, only more slowly.
- Using the manufacturing index alone as a proxy for the whole economy in a country where services account for the large majority of output.
- Confusing this meaning of PMI with private mortgage insurance, a completely unrelated product that protects a lender when a borrower puts down a small deposit.
Questions
People also ask.
What does a reading of exactly 50 mean?
It means the number of businesses reporting improvement is balanced by those reporting decline, so activity is flat compared with the previous month.
Who actually answers the survey?
Senior purchasing and supply managers at a representative panel of companies, chosen to reflect the size and sector mix of the economy being measured.
Why do financial markets react so strongly to it?
Because it arrives far earlier than official statistics and is rarely revised, so it often changes expectations about growth and interest rates before any hard data confirms the picture.
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