Many of our charts carry the label "not seasonally adjusted" in their source line or definition. This page explains what the label means, in the words of the publisher that prepares many of the figures we show, the U.S. Census Bureau. It describes how publishers prepare their figures; it is not about any law or rule.
Patterns that repeat every year
Some figures follow the calendar. The Census Bureau describes seasonal effects as effects that occur in the same calendar month, in a similar direction and size, year after year. It names the weather, administrative calendars and fixed holidays among the possible causes. Home building is one of its own examples: winter cold and storms leave a regular mark on new construction in some parts of the country.
What seasonally adjusted means
To seasonally adjust a figure, the publisher estimates those regular calendar effects and takes them out. The Census Bureau explains why it does this: the seasonal effects can be large enough to hide other movements in the figures, and a seasonally adjusted series usually makes neighboring months easier to compare.
The adjustment is itself an estimate. The publisher bases it on past years, and it revises the adjustment when new figures come in, so a seasonally adjusted figure can change even when the underlying count does not.
What not seasonally adjusted means
A figure that is not seasonally adjusted is the original figure for the period, with the regular calendar patterns still in it. When our chart says a count is not seasonally adjusted, the figure on the chart is the publisher's original figure for that month or quarter, not a version with the seasonal effects estimated out.
What the label means for holiday months
Fixed holidays are among the regular calendar patterns. A seasonally adjusted figure is meant to take their effect out; a figure that is not seasonally adjusted keeps it. So when a chart shows a figure that is not seasonally adjusted, a holiday month appears with its holiday effect still in it, exactly as the publisher reported it.
What our charts never show
Our charts never show a seasonal factor, the ratio a publisher uses to make the adjustment, and never show an annualized figure built from a single month. Every chart names its publisher, the period the figure covers and the date the publisher released it.
Where to go next
The Sources list below links the Census Bureau's own explanations. Preliminary, revised and estimated explains the other labels you may see next to a figure, how to read our housing charts walks through the source line, and our property search is open whenever you want to look at homes.