The cumulative return is simply the compound return of the series.

CumRtn(r₁, …, r_n) =

where r₁, …, r_n is a return series, i.e., a sequence of returns for n time periods.

StyleADVISOR uses the cumulative return over periods of one year or less. This is standard for GIPs compliance. The user can choose to annualize returns over periods less than one year through the Advanced Parameters (see Annualize Results: Less Than One Year).