There are several time-based methods for calculating absolute rebates. This page explains about whole rule period rebates.
The whole rule period method is unavailable for indefinite rules and rules that are longer than a year.
The cumulative total is calculated for the transactions from the start of the rule validation period up to the end of the calculation period.
Then, that cumulative total is put into brackets accordingly.
If the calculation period spans multiple years, the cumulative total is reset to $0 at the start of each year (as defined by the validation start date).