It can be useful to compare performance against a similar time the year before, or even against the previous week or month.
To do this, check the "Compare date ranges" checkbox underneath Date Range.
This will show two drop-down menus. The first allows you to choose which time ranges to compare:
"Previous period", where the current reporting period is shifted to end just before the current period begins. The number of days in the period being compared against is equal to the number of days being reported on.
"Last year", where data is compared against the previous calendar year. The start and end dates of the reporting period will be offset by one year. If either the reporting period or the comparison period contains a leap day, these two periods may have an unequal number of days. See further below for more details on how leap days are handled.
The second drop-down menu allows you to choose the means by which metric values will be compared:
"Previous value" shows the value from the date range being compared against.
"Change" shows the difference in value. For example, if total sales changed from $1024 to $1347, "Change" would show a value of $323, while a decrease would be a negative value.
"% Change" shows the percentage change relative to the previous value. A change from $1024 to $1280 would display as 25%, while a change to $512 would be -50%.
Matching on dimensions
Rows from the original reporting period and comparison reporting periods will be paired up ("joined") based on matching dimensions. For most fields, this matching is based on exact matches, e.g. a row in the original report with a Billing Country of "Canada" and a Product Category of "Toy" would match with a row in the comparison with a Billing Country of "Canada" and a Product Category of "Toy". In these cases, only combinations of dimensions present in the original report will be present: if there the comparison has a row with a Billing Country of "New Zealand" but the original report does not, that row will not be included in the comparison.
Some date dimensions, if present in the report, will be used to match up data between the two date ranges. Instead of matching exactly, the date value from the original report is offset to a corresponding date from the comparison period and then matched. For example, assume our reporting period is 2025-11-13 to 2025-11-19, being compared against 2025-11-06 to 2025-11-12. If "Day" was a selected dimension in the report, 2025-11-13 would be matched with 2025-11-06, 2025-11-14 would be matched with 2025-11-07, etc.
Date dimensions will be offset for matching between the original and comparison periods ("offset-matching") if the following conditions are met:
The field is a year, year-month, or year-month-day, e.g. 2023, 2024-05, or 2025-11-16 respectively. Year-week is not supported, nor are fields with a time component (e.g. year-month-day-hour).
The date field corresponds to the reporting period. For example, if reporting on sales, the date of the sale would be used for offset-matching, but the date the product was added would not.
The granularity of the date field must be at least as granular as the offset unit. In practice, this means that when "Previous period" is chosen as the comparison period only year-month-day fields will candidates for offset-matching (as the comparison period is offset by a number of days), while "Last year" will offset-match on year, year-month and year-month-day fields.
How offsets are computed
When Previous period is chosen as the comparison period, the length of the comparison period will match the length of the current period. If it is the 19th day of November, for example, and the reporting period is "Month to date", the comparison period will be October 13 to October 31st: both 19 days long. Similarly, if the reporting period is "Last month", the reporting period would be October 1 to October 31 (31 days), while the comparison period would be August 31 to September 30 (also 31 days).
When offset-matching year-month-day dimensions, the matching date from the comparison period will be determined by subtracting a number of days equal to the length of the reporting period.
When Last year is chosen as the comparison period, the start and end dates for the period will be shifted back by one year, e.g. 2025-02-24 to 2025-03-02 will be compared against 2024-02-24 to 2024-03-02, even though the latter contains a leap day and the former doesn't. In this example, if no date dimension is present, 7 days from the current year will be compared against 8 days from the previous year.
When offset-matching date dimensions, one year is subtracted from the date. E.g. the Year-Month 2025-11 will match 2024-11. In some cases, this can result in an "impossible" date, such as 2023-02-29. These impossible dates do not participate in matching: 2024-02-29 will not match against any day from the comparison period, and the "Day (previous)" field will be empty, indicating that a match is impossible. This is only a concern for "Day" dimensions: Year and Year-Month will always be able to match (although 2024-02's 29 days will be compared against 2023-02's 28).