Seasonally adjusted
A seasonally adjusted figure removes the regular pattern that repeats each year, so the underlying change in prices is easier to see.
A seasonally adjusted figure has had the usual pattern of the calendar taken out. What is left shows the underlying trend, without the rises and falls that happen at the same time every year.
The housing market has such a pattern. The number of sales and the prices achieved tend to follow a similar shape through each year, so a change from one month to the next can be partly seasonal.
Why the seasons matter
More homes tend to be bought and sold in some months than others, and the type of home that sells can shift through the year too. Families often aim to move in time for the school year, for example, and fewer sales tend to complete over the winter holidays.
If you compare one month with the month before, part of the change may simply be that pattern. Seasonal adjustment estimates the usual effect of each month from past years and removes it.
Seasonal adjustment in the House Price Index
The headline figures in the House Price Index are not seasonally adjusted. Seasonally adjusted series are published alongside them for the UK, its countries and the English regions. They are not published for counties or local authorities.
The index is also mix-adjusted. That is a separate step, which allows for the kind of homes sold rather than the time of year.
Comparing without adjustment
The simplest way to avoid the seasonal pattern is to compare the same months in different years. A change from March one year to March the next is not affected by the season, because both months sit at the same point in the cycle.
Comparing whole years, or a run of 12 months against the 12 months before, works the same way and also gives more sales to work with. Our guide to working out house price change explains the calculation.
Local figures
Sold price figures for a postcode district or street, such as a median price, are not seasonally adjusted. With few sales in a month, they are better read over a year than month by month.
Also allow for the newest month, which is always incomplete because sales take two to eight weeks to be registered. See why sold prices take months to appear.
| Removes | The regular pattern that repeats each year |
| House Price Index headline | Not seasonally adjusted |
| Adjusted series published for | UK, countries and English regions |
| Simple alternative | Compare the same month year on year |
Related terms
House Price Index · Mix-adjusted · Median price · Average price