What is it?
Many numbers follow the seasons. Home sales are high in spring and low in mid-winter. Store sales are high in December and drop in January. These moves come back at about the same time, and by about the same amount, every year.
Seasonally adjusted numbers have these regular seasonal effects, and calendar effects (how many weekends a month had, which month Easter fell in, and so on), worked out with statistics and taken out. That lets you ask, "Is this month really better than last month?" The original number without seasonal adjustment is called the raw (unadjusted) number.
With TRREB numbers (September and October)
These are actual GTA home sales from the monthly table in TRREB Market Watch, October 2026 (released November 4, 2026).
| September | October | |
|---|---|---|
| 2025 | 5,540 sales | 6,083 sales |
| 2026 | 5,034 sales | 5,603 sales |
In both years, more homes sold in October than in September. If part of that happens every year, a rise in the raw number alone does not tell you the market got better. That is why TRREB uses seasonally adjusted numbers to compare with the month before. These are the figures in the October report; TRREB revises past numbers later. For example, September 2026 was first reported as 5,040 in the September report and revised to 5,034 in the October report.
"Year over year" and "month over month" are read differently
- Year over year: October this year compared with October last year. Same month, so the seasonal effect is about the same, and raw numbers are usually used. TRREB’s "October sales down 7.9%" is this kind.
- Month over month: October compared with September. The two months are in different seasons, so seasonally adjusted numbers are used. TRREB’s "sales up from September on a seasonally adjusted basis" is this kind.
- So one release can say "down from last year" and "up from last month" at the same time. Both are true; they use different bases.
Reading the news carefully
- The gap between two seasonally adjusted numbers is not how many more homes actually sold. It is the change left after the change you would normally expect in that season is taken out.
- Seasonally adjusted numbers are revised later too. When new data come in, the seasonal effect is worked out again more accurately.
- Seasonally adjusted numbers still include surprises such as strikes or unusual weather. Do not decide "the trend has turned" from one month alone.
- Comparing the same month is not perfect either. Holidays that move, like Easter, or the number of weekends in a month can shake the result.
- The "seasonally adjusted annual rate (SAAR)" in housing starts data is the month’s seasonally adjusted pace turned into a full-year number. It is also used to compare with the month before.
What the law and official sources say
Quotes are copied word for word. The "In plain words" lines are our explanation, not an official translation.
A seasonally adjusted time series is a monthly or quarterly time series that has been modified to eliminate the effect of seasonal and calendar influences. The seasonally adjusted data allow for more meaningful comparisons of economic conditions from period to period.In plain wordsIn plain words: a seasonally adjusted number is a monthly or quarterly number with the effects of the season and the calendar removed, so one period can be compared with the next in a more useful way.
Source: www150.statcan.gc.ca/n1/pub/19-20-0001/192000012026001-eng.htm · checked Nov 4, 2026
As new data becomes available, the various time series components can be estimated more accurately. This results in revised, more accurate estimates of the seasonally adjusted data.In plain wordsIn plain words: when new data come in, parts such as the seasonal effect can be worked out more accurately, so seasonally adjusted numbers already published are revised to better values.
Source: www150.statcan.gc.ca/n1/pub/19-20-0001/192000012026001-eng.htm · checked Nov 4, 2026
On a seasonally adjusted basis, October 2026 home sales and new listings were up month-over-month compared to September 2026.In plain wordsIn plain words: with the seasonal effect taken out, home sales and new listings in October 2026 were higher than in September. In the same release, October sales were 7.9% lower than in October last year.
Source: trreb.ca/inflation-and-borrowing-costs-impacted-october-gta-real-estate-market/ · checked Nov 6, 2026
Common questions
Which is right, the seasonally adjusted number or the raw number?
Both. The raw number shows how many homes really sold that month. The seasonally adjusted number shows the trend with the seasonal effect taken out. Pick the one that answers your question.
Why does TRREB use raw numbers for year over year and seasonally adjusted numbers for month over month?
The same month has about the same seasonal effect, so raw numbers work for that comparison. Different months, such as September and October, have different seasonal effects, so those need to be taken out for a fair comparison.
Where can I see seasonally adjusted numbers?
In its news release, TRREB says whether figures went up or down from the month before on a seasonally adjusted basis. For detailed numbers, check Market Watch and the market data pages at trreb.ca.
Guides that use this term
Sources checked
- Statistics Canada, Seasonal adjustment: Concepts and interpretation, 2026 · checked Nov 4, 2026
- TRREB news release (November 4, 2026) · checked Nov 6, 2026
- TRREB Market Watch, October 2026 (mw2610) · checked Nov 6, 2026
- TRREB Market Watch, September 2026 (mw2609) — first-release September figure · checked Nov 6, 2026